*More unique and interesting powers and ways to kill people.
*a bit better storyline.
*Alex needs more of a solid character. He was a somewhat visually cool character, but his personality was bouncing off the walls.
*better graphics would add a bit more to the experience.
*Like somebody said earlier, Alex going insane would be cool.
*A sort of chainsaw like power would be extremely awesome.
*A bit more varied scenery and enemy/civillian design.
*Make it easier to execute those "HOW DID I JUST DO THAT" tricks, like when I used the groundspike attakc which sent a tank up in the air, which somehow hit a helicopter and blew it up.
*BETTER MUSIC. (although using my own music was still a bit nicer)