On foot controls like an FPS (Halo, Fallout 3, Half Life, etc) but with optional third person camera as well. I'm tired of having to hold a button to aim a gun, not being able to run backwards/jump and shoot
Make the player run automatically, enough wasting a button on sprinting!
More fluid transition when running and jumping, for instance currently when you are running and try to jump a wall, the Niko stops, jumps, grabs the wall, then lifts himself up. In real life, you'd jump and push off the top of the wall, hop over fairly quickly and be on your way.
Also, it'd be cool to be able to kick off a wall to change directions. You can use X for kick, now that its freed up