I haven't played other Classes that much, but I have played SW for a while now and I admit, that the mechanics of warlock is really kind of broken.
There are people out there on forums, youtube and ingame, who share the same opinions about the broken warlock. Well Warlock is known for hybrid class, that exceeds in no area, neither dps or heal.
I start off with some Confusions in Warlock mechanics and description:
1. The Soul spark & Soul scorch mechanics are kinda confusing, as you don't know whether you should equip Soul Spark in order to get more dmg or not. It apparently does, but it sparks confusion for new players. So you do can have soul scorch equipped, while having Soul spark mechanic active. Suggestion: Seperating Soul spark and soul scorch, would give players less confusion and more viable options. The soul scorch does very little damage in endgame content. It does minor AOE, but it is not noticeable. You could make soul scorch a AOE debuff power instead. Since the Warlock doesn't have much. As for Soul Spark the healing here is not really needed, since you got healers most of the time. For dps, you could either focus on pure dps build up or synergies with encounter powers.
2. At Will Powers: Hellish Rebuke, Hand of blight etc.
I feel like there aren't enough viable options for dps builds. 9 out of 10 times people are running the Hellish rebuke-no pity no mery-dust to dust build. Other builds are outshadowed. Because most of the guides leads to this build. So SW players are stuck to that same build and it eventually gets boring over time. Suggestion: I find a melee SW a hell ton of fun to play and it is a completely different warlock play-style as in most mmo's. Making Hand of blight abit more attractive would make him more versatile. Since warlock doesn't really take alot of punches upfront in melee like Tanks and other classes, you could switch the ranged and melee dmg of Hand blight. So instead of 25 (magnitude) melee and 35 ranged, make it 35 or 40 melee and 25 ranged. It is already punishing for warlock closing in enemies in melee and giving up save distance. The enemy dmg debuff is ok, 6% makes it even more attractive, but 4% is still ok. But what makes hand of blight in melee more fun is the speedy fast attacks and its animation is really pleasurable to watch. So please do not make changes to attack speed. Hand of blight with All-Curse consume and Deadly curse is a fun way to play, but in terms of dps it gets outshadowed by other builds and classes. so my SW applies for every fast attack, lesser curse to enemies and deals 25 magnitude dmg for each apply. Another suggestion, you could remove All-curse-consume and add it into hand of "blight". So hand of blight now also adds lesser curse on each hit.
3. Double scorch and power of the nine hells
As for soul scorched I already mentioned above. So both feat in this section doesn't really make a huge impact in dmg overall. 12 sparks instant gain isn't noticeable as full sparks only increase up to 4,5%. Suggestion: Power of the nine hells: reduces cooldowns of encounters by 8-10%.
Double scorch: increase or add more debuff to applied enemies or spawn minions for every kill
4. Creeping death and Executioners gift: This has been changed and balanced a few times. Maybe just add for executioners gift some numbers, like more dmg below "50%" instead of diminishing health. As for creeping death. I tested it out and it does 70-80 overall dmg on targets and when deflected even less, which renders it useless. A possible way to make creeping death great again is to synergies it with soul puppet, give him a new ability. if it's time consuming to script than just adjust the numbers
5. Dailies
Most of the time Players are running the first 3 basic dailies (without paragon dailies). I feel like the paragon dailies aren't nearly attractive as the standard dailies. Gates of hell is nice in pvp, but takes a long time to cast and sometimes hits in random direction. Flame of Phlegethos is ok, not great, but just ok. maybe add some Cool permanent summonings for warlocks. Since he is sort of summoner / necromancer. Also I'd like to mention there aren't any (permanent minions summoner) necromancers ingames like in most mmo's, it is demanding though
just a hint!
If you google for demanding necromancers in mmo's these days, you will find alot of people demanding it. alot of necromancers either do not summon any minions or just temporary ones, but i will cover this up in another post.
bonus: Infernal spheres could need some more love, but it is great as passive dmg dealer, aoe, and defense increase.
6. There are few general skills that are sort of squishy, but i will leave as it is
Thank you for your time reading it!