I got it today, and my impressions are thus:-
The graphics are spot on, though there is some slowdown in places. The missions are a lot harder that GTAVC.......I only finished the first one, the mission where you have to torch the restaurant is giving me a bit \'o jip. I spent most of my time on it this afternoon just driving round in a bus.
One area they could have made an improvement on is in including an in game map of some sort, or failing that, a simple compass that appears with the click of a button for 5 or 10 seconds or so. I found myself just driving round not knowin what direction I was going in.