Man, I’m so sad I didn’t play lock when MoP was live. I’ve been playing on a private server, just to see how it was, and I’m so jealous. I’m just gonna give a few examples of how amazing it was back then. Apologies for the wall of text that follows.
Let me first talk about the talents. The first four rows were ALL about survivability or utility. Nothing was about damage. Most of your damage was baseline, which is amazing in and of itself. The second to last row was about improving your demon; whether it was a flat damage increase, summoning a second demon for a short time, or sacrificing it for increased single target damage, max health and % health regeneration.
The final row actually changed your gameplay somewhat, and drastically changed certain spells. Giving multiple charges to Dark Soul, allowing you to move while casting your filler spells, or a 1 minute CD which gave you 500% increased AoE and 100% damage on your AoE spells for 10 seconds. This is how a talent tree should be. Utility or survivability, with very minimal damage increases or learning new spells.
Next I want to talk about the spells we had BASELINE, at least for the destruction tree. One thing to note, they used Burning Embers (BE) as the resource, instead of Soul Shards, but they are essentially the same thing. First you had Ember Tap, which costed 1 BE to instantly heal yourself for 15% max health, with no cooldown.
Secondly, you had Shadowburn, which was your execute at 20% hp. This costed 1 BE, just like it does now, however it didn’t have an internal CD. Also, it did more damage than your Chaos bolt if it critted. Chaos bolt does 3k damage, while shadowburn does 4.1k damage, just as an example (at level 73 with crap gear). You could cast this multiple times during execute, or cast on multiple dying targets, to keep all your BEs.
Now this next spell is amazing, and probably my favorite. Backlash - “Gives you 25% chance when hit by a physical attack to reduce cast time of your incinerate by 100%.” Last 8 seconds, and can only proc once every 8 seconds. Now this spell allowed us to be competitive against physical DPSers, such as melee and hunters. This spell alone would make us viable again in PvP.
One thing that today’s warlocks don’t have a lot of are instant cast spells. Aff locks don’t have any direct damage instants. Fel Flame is an instant cast that generates BE, with no CD or charges required. We also had Backdraft and Dark Soul: Instability both baseline. No talents required.
Finally, we have Soul harvest. This allowed you and your pet 2% health regen every second while out of combat. This made it super easy to continue from pack to pack while leveling. Also made it so that my pet doesn’t feel as much of a wet noodle, as I didn’t have to health funnel after every pull of 3 mobs.
There is also quite of few spells that each individual pet has, that made it unique. For example, your void walker has disarm, which is amazing to be able to cast against a melee. The Succubus has Whiplash, which knocks all foes back 5 yards. Little things like this made each demon useful in their own way.
TLDR: Most of the talents were about Survivability or Utility. Most of the spells were baseline, and included a bunch of useful spells no longer in the game. Demons were more useful and had variety. Warlocks didn’t suck against melee.