Grand Theft Auto IV thrusts the player into a world created by the people at Rockstar. A world that is completely original and full of wild and kooky characters, and yet it is a world that feels very familiar and not artificial like many other games feel.
As in the other games in the GTA series, you can run around in sandbox-style play and do basically "whatever the hell you want". The games environments are beautiful, there is a large assortment of cars, trucks, helicopters, and other vehicles, and lots of comedy. However, while environments look amazing, character models look pretty rough at times. Facial expressions are very good though, showing emotion and telling a whole story in themselves.
There are the few graphical glitches and bugs, but for the most part, the game runs extremely well. There is little to no texture pop-in, lag, screen tearing, etc.
My only gripe with the game is that there is nowhere near as much character customizing as there was in San Andreas.