What's the problem with Warlocks? Honest question. I've been considering playing mine as my main in Legion, but haven't done anything with it yet and I'm curious.
All 3 specs in MoP were amazingly fun to play and rewarding. All of those playstyles have been completely changes in large mechanical ways by this point. I don't know a single warlock who didn't like what they did with all the specs in MoP, so its very disappointing to lose those playstyles even further (it began in WoD).
Off the top of my head..
-Destruction no longer has a Fire and Brimstone which lets all of your spells AOE at the cost of secondary resource.
-Your secondary resource (burning embers) has been lazily changed to soul shards which is what all the other warlock specs use.
-Green fire animations for spells have not been updated and use the old animations instead of new ones that the standard spells use.
-Rain of Fire was changed in WoD to no longer generate burning embers
In MoP, Destruction was an AoE monster, it was very fun to gather a huge mob pack and AoE them all down with self sustaining secondary resource generation via Fire and Brimstone and Rain of Fire.
I can't speak much to Demonology but:
-No longer have awesome Meta Demon form (which changed colors to green when you obtained green fire).
-Now has horrible 10 second long maintenance buff for demons which are only out temporarily for 8~10 seconds.
For Affliction, I did not play it much but in very late MoP we lost the ability to have our DoT's Snapshot (or was it WoD?) which killed a lot of the fun of that spec for me. Casting your DoT's when you had everything proccing could lead to some insane damage and you could soul swap that set of empowered DoT's around to multiple targets in multi-boss fights. It led to crazy insane DPS disparities between the best and worst players and I believe was instrumental in Blizzard deciding to remove DoT snapshots. You also used to be able to AoE pretty decently with Seed of Corruption, but its changed so it hits like a wet noodle now.
The fact that a lot of this coolness was taken away and given to another class (Demon Hunter) and they are touting this expansion as a return to "class identity" is a total slap in the face to Warlocks who already had their Class Fantasy taken away by Legion and WoD's changes.
Okay, rant over.