Honestly I don't like many of the changes. My thoughts:
Affliction - As stated, the loss of Drain Soul is huge. The skill is far too iconic to allow it to be slipped in with pruned skills. It's just not acceptable. It feels good to pump out crazy damage once the mob is in a weakened state. Everything makes sense and they need to revert that ASAP.
I'm agreed on the fact that with snapshotting in WoD, Affliction will be a bore in its current state. I'm not worried though. I can't see Blizzard allowing Affliction to be a super easy and uninvolved spec. Looking forward to seeing what new mechanics they add to spice it up.
Demonology - Why Carrion Swarm, why??? Such a cool ability tied to a different skillbar, which means that you don't need to prune it. Having options in Meta form is fantastic. Losing Void Ray on top of it makes gameplay during Meta uptime less exciting. Given, I never really liked Void Ray and I always thought it played out pretty clunky. It got the job done, but it left much to be desired. With the loss of these abilities *and* snapshotting, I feel like Demonology will be much less intimidating for people who always wanted to try out a pair of wings, but didn't want to be abused for not pulling off the numbers people expect to see.
Destruction - While Immolate has been buffed greatly over the expansion, I don't feel people worried over much about snapshotting it as well as possible. People who played Destruction on the daily got a pretty good feel for it. It's the only DoT you have to manage. That is to say, going forward into WoD, the loss of snapshotting won't feel like a huge hit in gameplay.
I don't understand the meaning behind removing mana gains from Shadowburn. They said they simplified it, but it looks like a straight up nerf. It's not like I'm calculating my mana gains on the fly while using up Shadowburn charges, I just know I'm getting mana back at an increased rate to supply the increased amount of Incinerates you cast during the execute phase. Are they trying to balance all the specs on not worrying about the low HP burn phase? If so, is Soul Fire exempt because it isn't as comparatively strong as Drain Soul/Soulburn? Maybe they are just sick of balancing classes that excel in that aspect. If that's true then I'm a little disappointed because I look forward to finishing off mobs like that. It's actually pretty fun. I'd love to see the reasoning behind those changes.
General - I like the simplifed gateways. It was needed for balance, so the 1.5 min CD seems legit. Warlocks no longer seem necessary for Healthstones, due to the overall nerf to self healing during an encounter. The nerf of course being you now only get one use of a healing consumable. I *do* like the baseline curse changes, that's a huge quality of life improvement and possible balance for losing some of our raidwide Warlock perks. (HS/Gateway)
The only other questionable topics for me are Fel Flame and Soulshatter. One is pretty damn nice on the move and the other is a safety blanket due to our insane DPS output. It makes you wonder if Demonology will lose their taunt due to it being tied to Soulshatter. Here's hoping they add in other outlets to pump out DPS while on the move with the loss of Fel Flame.
All of the above is not taking into account the new talents and how they work with these changes.