I bought a PS3 specifically to buy this game and I don't miss my 500 bucks.
The in-vehicle stuff is pretty much unchanged (I haven't had a problem with the physics; sports cars handle fine), except you can fire in all directions. Plus, no more planes (too much 9/11 potential I guess).
But the on foot stuff is upgraded beyond belief. The aiming, the pedestrians, the world around you, the side missions and mini games are all lightyears beyond San Andreas. Probably gonna play this every night until Metal Gear Solid 4 comes out, then switch to that.
But yeah, a must have.