Good storyline, even better online.
It may sound back breaking at first. Shoot 200 flying rats (pigeons), jump 50 or so stunt jumps perfectly, take all your friends out to every place on the map, etc, etc.. but as soon as you get into that mode of "gotta get 100%" none of that silly outdoors stuff matters anymore! Feeling the rush of being truly free is something you don't see a lot in video games, still.
But you don't have to be in a mode to enjoy this game ether. You can do almost whatever you want! Date a girl on the net, then do her "hard and sloppy" then next day. Go bowling, racing, pool...ing