Warlocks had it pretty rough
1) Free kills in PVP. The only defensive tool we had, fear, got nerfed in PVP because players didn't like that their free kill could make them run around helpless and actually stand a chance of fighting back. But rogues stunlocking you until dead was perfectly fine from Blizzard's PVP design philosophy. Derp.
2) Useless pets. You basically had imp out to give people more HP in raids, or you did a spec where you sacrificed your demon to boost your DPS. There were very few encounters where felhound, voidwalker, or succubus actually had a usage in a raid environment beyond being a voidlink sponge or the rare crowd control fights.
3) Useless specs. Lots of classes had to deal with this, but warlocks had it pretty bad. Demonology was pretty worthless outside a couple talents. Heavy destruction was also pretty worthless DPS wise early on, especially since bosses/mobs used to have elemental immunity, rendering all the fire based spells worthless.
4) Infernal and Doomguard was never worth the risk (since they would eventually break enslave and become immune to it and kill you) and had too long a cooldown in any event. Doomguard Russian Roulette was pretty lol, though. Too bad you could only do it once an hour.
5) Shard management. It went from 1 shard per mob that gives XP and no special bags, then they added special bags (the good ones were very expensive to make and hard to get drops), then much much later they added the multi-shards from a single drain. It was a pain in the ass because they didn't stack and you needed a fuckton for raids.
Killing yourself with hellfire was nice, though, because you didn't take durability loss. We'd always do that when a raid wipe was happening to avoid having to spend more money. Spam lifetap, hellfire, dead lol. Warlocks also did have lots of nice utility, which always made them useful to bring along. And high HP helped for the AoE fights so you could live longer.
Funny part is I originally never intended to be a warlock. When Tigole invited some of us to beta, hunters weren't in and for whatever reason, I thought hunters might be the most "monk like" (idk where I got that idea, at the time druids had feign death). So I figured I would play warlock since I could learn pet management on the class at the very least. I ended up liking a lot of their utility, so I ended up just sticking with warlock until they actually released monks in MoP.
