When I'm playing warlock, I’m usually just spamming Eldritch Blast, which gets a bit boring after a while. So, if you want to make warlocks more fun and tactical classes, bring back Eldritch Essence and Blast Shape invocations from NWN 2, which can be applied to an Eldritch Blast. You could even improve them further.
Eldritch Essences modify the damage or other effects of Eldritch blast. For example, Hellrime Blast deals cold damage and adds a dexterity penalty to the target. To make it even more fun, it could be changed, so that it can freeze targets.
Blast Shapes modify the range, number of targets, or area of Eldritch blast. For example, Eldritch Chain jumps from the first target to others.
So, if you use both Hellrime Blast and Eldritch chain, your Eldritch Blast would do some cold damage and freeze multiple enemies.
Overall, I think that Eldritch Essence and Blast Shape invocations would make Warlocks much a more versatile class to play.