My son has been IMMERSED in GTA4 for days .... on xbox360.  I have looked over his shoulder and actually wrestled the controller away for a few moments.  Driving is a bit squirrelly, takes a bit to get used too.  Read in a forum that some folks say the ads (as usual) show better graphics.  For the best look around hold down the B key and you'll get cinematic views of the surroundings (while driving).
If you have ever driven around Manhattan this game is scary!  You will recognize street corners, buildings, -you get a feel for heading uptown or back to the bridges. Even if you don't go around bashing folks, this is a great NYC simulation with a lot of detail to say the least.
-  Bill .