My biggest gripe right now is that the mouse, while driving, is in permanant "free look" mode -- I hate that. When I turn the vehicle, I want the "camera" to follow the turn AUTOMATICALLY - I don't want to have to turn it with my mouse to keep from getting screwed up mentally about the direction I'm actually headed in!
FYI - I discovered a solution to this (kind of). When driving, as long as you don't actually MOVE the mouse itself, the camera WILL follow the vehicle in almost the same fashion as it did in previous GTA releases.
It doesn't seem to have quite the same "snap" to it, but it's better than nothing, and has made it a little bit easier to control. It's hard to not move that mouse when your handbrake is bound to the RMB, though! I might have to bind an additional key to the keyboard, but that would just feel weird.
I really do hope they add in an option to disable this feature in a future patch.