I'd be hard pressed to find anything I would've done differently. Maybe make it an XBLA/PSN title with superior visuals but to be honest it looks fine already.
 
The campaign is a blast to play, the multiplayer seems solid, there's absolutely nothing majorly wrong about this game. It's a really well crafted package in every way. 
 
Although - the nightclub scene gave me a really bad 90s flashback when I discovered all the "dancers" were actually 2D sprites.  Almost made me offer a dollar bill and utter "shake it baby".  I fucking hate 2D sprites in 3D games. But that's my only real complaint and I struggle to find more! I hope it sells tons of copies!