I really dig the split screen. Took a little while to acclimate to the distance at which it activated. Personally, I think my brain wanted it to transition more gradually, and initiate at a further distance (current resolution: 1920x1200). Perhaps the implementation of a variable slider, to fine tune the distance it initiates at based on preference.
Pause menu has legibility issues, what with how chunky it is and all of the movement.
Controller mapping (Xbox360) was a little akward. Left analog stick would only move my character up, down, left & right. Aiming was mapped to the right analog stick. This wouldn't be so awkward if actions were mapped to bumpers or triggers, by default, instead of/in addition to the face buttons.
All in all: fucking rad. The demo mode is a nice touch.