I've been playing 4 recently and I'm a huge fan of the psyker drugs mod. It's basically a glorified cheat gun that gives you magic beams and unlimited stealth boy, but I actually find out rather well balanced. The ability count as either grenades or chems, they use AP instead of ammo, and you have to be able to access the institute to unlock them. Plus, they start out weak and to make the stronger you have to produce stronger variants that do more and more damage when you take them so if you can't handle -250hp in a Chem you just die.
I haven't used all the powers yet but psychic ice blast and teleport are just so much fun. There's a psychic fist that's just a powerfist with the model replaced with warbly purple energies. Having AP based jet for parcor is also just a blast.