You can flip cars (was very surprised there), the sub-mission (taxi,vigilante) are all in, the explosions and smoke effects ROCK, the gunfights are fairly easy to control, the cops are hard when you get 3+ stars (try busting through some of those roadblocks, they stop you dead in your tracks then they swarm you)
Each car has its own music track, some probably share the same but I cant tell, the music is nothing special but then again I wasnt expecting anything but got something at least. The camera movement can get annoying in some areas but you get used to it.
The framerate is pretty bad sometimes, but it does not ruin the game, it just shows the GBA's limitations. When you got 5 cop cars and 10 cops running after you all firing it can slow down pretty bad, but its still hectic and even a little helpfull because in all that chaos you need it to go a little slower.
The gameplay itself feels exactly like the old PC games, with the new features of the PS2 ones thrown in for extra measure, so far I've done about 10 missions and have like $20000, to give you an idea of how long I played, its addictive and fun, I like what they have done here.
The biggest downfall so far? I'm 15% complete according to the game stats, and I've only been playing about 45 minutes.
IGN Review:
http://gameboy.ign.com/articles/560/560417p1.html