I think that the graphics are better on GTA IV because of the redraw rate. You can see much further on GTA IV. But, it's a minor issue with me. I've always been more engaged with game play than super shiny graphics. But, at the same time, I'm playing on a somewhat new LCD T.V. but in 720p. So, you're probably seeing a lot more polish than I am.
Either way, I really like the game. The battles are epic and pretty tough too.
X-Play just gave the game a 3.5 out of 5. Adam Sessler said it was a solid release.