I think San Andreas was more fun and a better game (huge game area, diverse locations etc), but GTA4 is one you still can't miss I think. The Rockstar GTA humour is still there, the plot is good, characters are vibrant and detailed. The only downside, and the reason why it gets so much flak, is that the performance (on both consoles and PC) was poor. You need a decent quad core CPU to run it as smoothly as you may play your other games. Saying that, I completed it on a Core 2 Duo E6750 and a Geforce 8800GTS 320mb (!!), so it's not the end of the world, and I still enjoyed it. However, after getting a Q6600 and GTX280, it was even more enjoyable.