This is the deepest game I've seen so far. The environment is wide, and you can do anything, from playing pool, to watching tv for 20 minutes of funny stuff, to surf the net, to read and send emails. Even junkmails have working links that lead you to very funny web sites... It's like The Matrice.
Still, the main story is also great, and in the GTA tradition, you have to steal and drive all kinds of cars, while listening to hundreds of mp3s on the radio... I spent hours driving around without a goal, just causing havok and running from the police for the fun of it.
There's something for everyone, and hundreds of hours of fun gameplay.