I will agree that they are rather feat heavy as many of the archery feats help aid a Warlock in its Eldritch blasts but gear can help as well. Chausible of Fel Power (Major) adds 2d6 to your Eldritch blast. This is like adding 4 levels of Warlock to your damage. The limit on the damage is to offset the other abilities they get. They aren't going to be the primary nuker like a Sorcerer or Wizard but do more damage than your tanks. Add in the blast shapes like cone and chain and such and you are getting some AoE with your blasts. You can also apply add an essence to it as well. Imagine chaining an 11d6 (level 20 w/gear) Vitrolic Blast that ignores spell resistance, adds 2d6 acid for 4 rounds stackable with up to 1+5 targets or use a cone shape to hit an even larger group. These aren't even the highest invocations. You could be giving targets negative energy levels, run around as a horned devil or have undead minions like a Necromancer. Here is a list of invocations http://nwn2.wikia.com/wiki/Invocation. Your primary weapon is going to be doing more damage than your sword weilder with the possibility of only the rogue out damaging you if they can backstab. (I've seen nasty builds for 2 weapon backstabbing rogues that will put a wizard to shame if they get their full attack going with backstabs). Maybe a dual weilding fighter with awesome elemental equipment (+5 swords with Fire, Frost, Electricity, Acid and Sonic) and high STR or a well built archer with the feats and similar elemental bow but they will need to hit the target. Even decked out with good equipment monsters at high level can have insane ACs. The warlock only needs a touch AC.
Keep in mind that balancing the damage output is that fact that you can keep doing it over and over and over. A caster type is going to run out of those big spells and be reduced down to nothing in a long battle. They also aren't able to take hit very well. The fact that the warlock can wear light armor, has a d6 vs a d4, gains energy resistances to 2 things up to 20 at level 20, up to fast healing 5 for 20 rounds at level 20 and DR/cold iron up to DR5 at lvl 19. Their saves are poor but there is an invocation that gives them their charisma bonus to their saves like a Paladin. Their REF save should be high from a high DEX.
You are have the ability to use wands and scrolls early on with a bonus even. This lets you add your versatility in equipment.
The part that I could complain about is that even at level 20, you are allowed no more than 3 of each level of invocations for a total of 12 (if my source is correct, I'm using a NWN2 chart for abilities). Even into epic levels this does not increase. It forces you to stick with just a few tricks.
Question, does haste allow the Warlock to blast twice? I know it doesn't let casters cast twice but a Eldritch Blast is considered a spell-like ranged weapon. Maybe not because of the spell like descriptor?
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