I bought a PS3 and GTA4 on Monday. I've been enjoying it, but it's definitely lost its charm or something since the previous GTA games. That's probably not just the game's fault; I've found that as I'm getting older, I'm less bothered about games and it's only a specific few that I actually find myself engrossed in (the HL2 titles, for example). That said, there's definitely something that the game is lacking. I just feel no urge or motivation to drive around, explore, go crazy, and just do whatever I want.
It's a great game, don't get me wrong, and maybe if I'd been playing it 4 years ago or something when San Andreas was around, it'd be different. But then, my circumstances were different too; I was bored a lot so it was easy to just sit there and play it for hours.