Warning this turned out pretty long but it's all constructive feedback so bear with me :D
 
Ok first of I want to say that I really like the new Disc Priest. I never played priest before and the main reason I even got Legion was to play Priest and go Disc because it seemed cool and reminded me of other games that have had similar DPS heal transfer typ healers.
 
I really enjoy the hectic play-style and high skill cap of the specc, mixed with doing damage, changing targets constantly etc, instead of the classic "Health bar Whacka-mole" game the other healers play.
 
With that said I feel there are some major issues with the specc and some of the design. Contrary to what most other threads on here whining about Disc Priest I actually don't care to much if it's the "Best" or the "Worst" healer or generally how it compares to the other classes or speccs.
I think it's kinda fine where it is in terms of overall power atm. I have been able to complete the things I've tried (for example +4 bolstering VoW almost getting the 3 chests, +6 bolstering Maw etc, at an iLvL of 840 with random pugs) so It's definitely not as terrible as some people claim, I haven't played any other healer in Legion yet (never even tried speccing Holy yet) so I don't really know if it's waaaay easier for them or not.
 
So why am I whining then?
 
Because a lot of, in my opinion "stupid" design things make Disc a lot less fun to play than it should be, and it doesn't have to be that way. It feels like they made a cool idea and plan for a specc and then never really finished it or thought through all the details of it.
(Now a lot of this is mainly aimed towards Mythic+ but applies to raiding to some degree as well)
It's supposed to be the DPS healer, this is what differentiates it from all the other healers and makes it unique, yet to be effective and actually succeed in healing Mythic+ you pretty much have to play the Shadowmend + Shield health-bar spam game (yes I know this may be different in raids) throwing in a penance when time allows.
If it's supposed to be a niche role then make it at least decent at that role. Now I don't mind spot healing every now and then, that's completely fine, I understand Disc aren't supposed to be great Tank healers but Spot Healing shouldn't be the majority of the healing giving us no time to actually DPS, which is IMO what Disc should be doing most of the time. A holy paladin can pretty much out DPS a Disc priest in Mythic+.
 
The play-style of Disc should IMO be much more rewarding when playing the proper "atonement up-time flawless DPS rotation weaving in a Shield or Shadowmend here and there to burst up someone and apply Atonement" rather than regular spot healing. If I wanted to spot heal I would be playing Holy Priest right? And maybe I'm stupid for playing Disc when Holy might just be strictly better, but I want to play the one I find challenging and enjoyable.
 
So get more Mastery to make your Atonement heal more when you DPS you say?
Well no because Mastery sucks. I can already increase my Atonement healing by just doing more DPS with Haste and Crit which also actually benefits all the Shadowmend and Shielding I have to do anyway. Why is Mastery so useless? I don't think even if it increased ALL healing done it would be worth it.
 
And this is where we come to my main issue with the whole Disc priest and why I feel it's not "Finished" or "Polished" as a whole. Why are there so many things about it that just feel completely useless, uninteresting and boring, like Mastery.
 
First of we have the Talents. Here I feel like there's very little choice or really anything interesting to choose, and they just overall feel really bland.
 
Tier 1: Castigation really is the only choice here. The penitent is just plain terrible and further pushes the "Spot healing" theme which we are not supposed to be doing. Wasting our only good DPS ability to single target heal someone instead is just wtf in the theme of the specc. Schism of course has some sort of use and maybe if the DPS healing was stronger this could fit sometime.
 
Tier 2: Utility stuff that's really up to personal preference. Even though I feel this tier is boring it may actually be the best designed one IMO, since really all of them feel like something I would choose in various situations. None of them feel useless compared to the others, GJ.
 
Tier 3: Again a fairly poorly designed tier where it feels like Psychic Voice is always the answer. Shining Force can of course be good sometimes, especially in PvP and I'll admit I've never even tried Dominant Mind.
 
Tier 4: Both good and bad I feel. The talents are all somewhat interesting and would be nice to pick but the problem is that Mindbender is just crazy strong making the others useless.
 
Tier 5: Here we have an actual choice to make, Power Infusion or Twist of Fate?
Power Infusion being the more fun and generally useful pick. I don't like the design of things such as Twist of Fate that really just "rewards or compensates" you for bad play. I'd rather have something that buffs you if you manage to keep your team UP, performing your role well. This also suits Disc play-style better since the main goal is pretty much to keep your team healthy and avoid panic situations where you're forced into Spot heal spam, this talent just promotes that "non disc play-style" again, similar to The Penitent on tier 1.
Contrition is just bad, if it had a longer duration it could maybe be useful but it also feels like a boring choice that only serves to lower the skill needed to play Disc.
 
Tier 6: This one feels pretty boring overall. Halo is useful in Raids, Divine Star is not really that useful in general but it's our only AoE choice, would be cool if atonement at least healed part of AoE DMG and not just the first hit. Clarity of Will I guess is considered garbage by most. I've actually tried it in Mythic+ and found it to work pretty well but really it's just a slower Shadow Mend and again it just forces you even closer to being a Spot healer like the others.
 
Tier 7: Now this is where you have your first and only real choice to make it feels like.
Do you go Purge the Wicked or Grace? You want both! That's great this is what choosing a talent should feel like!
However, Grace again is another talent that just pushes you even closer to the Spot healing play style and away from what Disc was supposed to be! Why isn't this giving +30% healing through atonement healing instead? (must ofc not be +30%) to promote our intended play style?
Purge the Wicked is probably the coolest talent Disc has together with Power Infusion. It promotes the DPS healing play style, has synergy with our main DPS ability Penance, rewards multi-dotting active play style, takes some skill to keep up on many targets and at all times, Good Stuff!
Unfortunately Grace is almost always better (not in raids maybe) since Spot healing is pushed so hard.
And then we have Shadow Covenant... Yea this just sucks in every way. Even if it didn't have the heal absorb drawback it still probably wouldn't be picked because it replaces Power Word Radiance, our only AoE Heal and Atonement applier, Wtf? Shadow Covenant should at the very least apply Atonement to everyone it hits, letting you heal them 6 sec later with Penance or something, creating some sort of strategy for using it and actually promoting the Atonement DPS play style rather than a crappy AoE Spot Heal.
 
So to summarize the talents: Boring and no real though in what you choose. Almost nothing to customize according to personal preference. To many things that just encourages you to NOT play Disc priest the way it's supposedly intended and those that do are just to weak (Schism, Solace, Contrition, Divine Star).
I would much like to see a talent that gives you a buff to place on someone increasing Atonement healing that person takes by say 100% to use on tanks or someone about to die, rather than crap like Grace that just makes you wonder why you're not playing Holy if you're going to play that type of healer anyway.
 
And now for the even more boring choices; The Artifact Traits!
 
What the hell is this? Does anyone find these interesting at all? The only trait in the entire tree that is fun is Power of the Dark Side, this is a good one. It makes something happen to react to, it promotes multi-doting, it promotes DPS heal via Penance and it's actually useful! Nice. Borrowed time is also a good one for pretty much the same reasons.
Then we have the big one, Sins of the Many... This is a pretty strong trait, don't get me wrong but it has a major flaw. This is supposed to be pretty much the ultimate trait for Disc yet it kinda sucks at all times except for Raiding. Getting a buff of +1-5% damage when in a group or solo is pathetic and you can pretty much ignore the effects of it, putting Atonement on someone who doesn't need it at that moment isn't worth it, casting another smite or whatever is a better use of that time and mana.
Why doesn't this work like some of the other healers abilities where it's power is increased in non raid situations, like Tranquility with it's 100% increased healing when not in raids. It could give at least +3-5% damage per Atonment when not in raids, making it about as potent outside of raids as inside. Also promotes keeping Atonment up on your group for the DPS increase if your mana allows it.
Apart from these traits the rest are just completely uninteresting and only serve to take you the fastest way to get these 3. Since Power of the Dark side is on the Right side, this side is really the only path you would ever take in your Artifact tree. There is pretty much zero choice or customization involved regarding the Artifact. The Shadow Artifact traits feel a lot more interesting since there are some actual play-style defining alternatives to choose from and you actually want all of them but have to choose :).
 
So to sum the Artifact traits up:
Super boring, no real choices to make, nothing that defines or changes the way you play at all. Biggest trait is pretty much "raid only".
 
This of course brings us to the inevitable complaints about the Artifact ability itself.
I've seen plenty of fighting about this on the forums already and I have to agree with both sides. It is Not a super weak ability as most claim.
It is however a super boring ability with a way to long cooldown that, again is really only good in raids! At the very least this should also go from a +10%/Atonement to a 30-50%/Atonement buff when not in raids, just like like Sins of the Many.
Using the Artifact in a 5-man or when solo deals damage like a Penance but slow and clunky and Heals less than a Shadowmend if you want to burst the Tank up or something.
I would personally much rather see this ability reworked completely to give it some interesting mechanic in line with the Shadow version, that one is cool. Right now it's just a Slow, Long CD, Immobile, Raid Specific, Mediocre damage and Mediocre heal when not in raids (or if you don't have sins of the many in a raid). It is basically a Shadow Bolt from Vanilla wow but with 90sec CD.
Give it something special, something that promotes the Atonement play-style, something fun and interactive.
Some example could be "When used refresh the duration of all your Applied Atonements" or "Increase the Duration of all Applied Atonements by 10 sec" or "Debuff the target for 5 sec giving everyone who attacks it Atonement" or "Increases healing done via Atonement by 100% for 10 sec" Just something that doesn't make it feel like I'm casting a Shadow Bolt in vanilla wow when I'm using my "ultimate" ability. A shorter Cooldown would definitely be preferred but that would of course have to depend on how strong it is. Anyway make it FUN to use not, Meh guess I may as well use this once in a while.
 
Ok Sorry that was a very long Rant :) but the summary of it all is:
I really like the new Disc priest and I just wish they would push the active good DPS heal, new play-style it was intended to have rather than make every choice an option to revert back to the usual type of healing making you wonder why you would't just play Holy instead. All in all it feels like a great concept for a fun and different healer experience that unfortunately seems to have been forgotten along the way.

I'm totally ecstatic for the progression potential of mythic 5mans in Legion, and want to master the changes to prep. So I ran some Mythic dungeons tonight and would be eternally grateful for any advice from any of the experts out there :)
Here are my logs:
https://www.warcraftlogs.com/reports/wCfk4zX8m3AZJP7g/
And Armory, definitely not fully geared, but pretty decent for mythic dungeons: 
http://us.battle.net/wow/en/character/stormrage/Ziltana/advanced
Overall, how are my numbers looking? Decent for this gear and content? 
 
Some specific things:
Am I casting Regrowth too much? It feels much more important now with the mastery stacking, but I'm not sure if it's worth the mana especially once fights start getting longer.
I also feel like I'm replacing HoTs a little too early. Should I basically be aiming to recast Hots as late as possible, or is it more important to keep their durations high at the cost of efficiency?
And lastly, should I worry about my overhealing? If so, what can I do to try and lessen it while maintaining hps?

LOG: https://www.warcraftlogs.com/reports/TA2vBqcFfm8aVpXn#type=damage-done&fight=27&source=3
 
I hope that links right - I have no logs on Butcher/etc, but this is the most stand-still raid encounter I can think of. I hope that's okay! I didn't have to do more than a little moving, and this is pretty indicative of my DPS in most encounters that aren't a lot of cleaving or movement (My dps is pretty bad in fights like Xul'H or Iskar as well, but they're probably a lot harder to read)
 
Armory: http://us.battle.net/wow/en/character/bloodscalp/Sunfury/simple
 
As you can see, I have a mix of mythic dungeon, heroic and normal HFC gear, and a few pieces of baleful I'm not yet rid of.
 
normalized stat weights given by my own simcraft runs are
 
Int 1
Spell Power: .89 (due to archmage's ring)
Haste: .57
Mastery: .67
Multi: .62
Crit: .57
Versa: .51
 
My rotation is the same as the one listed on icy veins/altered time/etc -> I do admit that I make some mistakes, sometimes I split a cast on a crystal and it despawns before the cast lands, sometimes I supernova when I could have held it for my next crystal, etc.
 
1. Prepot on pull
2. stack Arcane Charges to 4/let boss get positioned
3. Drop crystal + arcane power
4. PoM Arcane Blast + 2 Super novas
5. Arcane Blast/Arcane Missile to 50% mana
6. Evocation
7. Stack AC to 4
8. Expend missile charges
9. Arcane Barrage
10. Repeat 7-9 until evocation has 20sec left
11. Drop Crystal + charge and commence burn phase
 
With Supernova being used on cooldown when I'm not really close to 50% mana or have a really good reason to hold it (like crystal coming up soon, or lots of adds soon)
 
I realize that I only have the 690 ring and don't have any good trinkets, which is a big deal, but that can't account for all of my crappy DPS - I'm looking at my log rankings and they're all <20th percentile for my ilvl, so I must be doing something wrong.
 
Any help would be great!
 
edit: Added video https://www.youtube.com/watch?v=MCdL7F_kAuU

I wasn't able to play WoW due to irl reasons for the last five months but I still had my subscription active. Mainly because I kept forgetting about it but also because I love the game and it's always been my pleasure to support Blizzard.

However lately I don't enjoy some changes they've made. More importantly the way they stubbornly choose to "ignore" %90 of the player feedback. I know that individuals affiliated with Blizzard try to respond to most posts and tweets, I do appreciate that. However almost none of these affect the game in any way.

I couldn't help but notice how they started to pay more attention to player feedback in general and actually implement some changes accordingly after the Q1 sub loss.

If it takes another -3 million subscribers to really get their attention, I'll gladly be one of the many. Consider unsubbing for only 1 month, maybe then will they remember WoW's success came from catering the players' needs rather than shareholders'. Maybe then will they become less Activision and more Blizzard.

Lok'tar ogar!

logs: https://www.warcraftlogs.com/reports/tfgT7pBvW36NH91F#type=damage-done&source=17&fight=6
 
armory: http://eu.battle.net/wow/en/character/sylvanas/Anf%C3%A1uglith/advanced
 
Any suggestions as to how I could improve? 

Also, I have a question about Dark Transformation and Blood Tap. Should I prioritize Death Coil over rune capping when DT is off? Is it sub-optimal to recharge an Unholy rune with Blood Tap in a single-target rotation?