GTA:IV was not ready for the PC. Unless you are use to using a XBox 360 controller, you might be disappointed. This game reminds me of those cheap games that uses a 'fixed' controller set-up. RockStar just now came out with a patch that allows you to re-map buttons on a couple of racing wheels. I am hoping their next patch addresses re-mapping keyboards and mouse controls.
I've never hated a game I love to play as much as I do this one. It is a very buggy game. My opinion, if you have an Xbox you should run to the store and buy this game right now. If you don't have one I would wait until they fix it some more.
I really love the game, but I almost dread playing it because it is such a pain.