I bought this some months ago after playing the 20 minutes limited demo available on PSN.
This is without doubt the most fun I've had on the PS3! Forget Black Ops (overrated, IMHO), this is what action is all about. The first time you use the grapple wire to connect your car to an airliner taking off, and watch it swing around in the aircraft's backdraft, I defy you to have an almighty grin on your face! The challenges are varied and not too tough or too easy, so the game kind of grows with you. And there is no single way to complete any given mission, either. I played one mission as to obtain some GPS coordinates as though it were a stealth mission, and only went trigger happy when I found I had to kill a guy with a passcard for a locked door. Superb fun. I even spend many hours just hijacking fighter jets and apache gunships and laying waste to the beautiful (and its really is beautiful) island of Panau, instead of tackling missions.
Fans of TV series "Lost" even get a special treat in the guise of a hidden island to the North West of the main play area (which is over 200 sq km in size). This is truly a game to get lost in. Buy it, enjoy it. I'm over 50 hours into the game and have only completed about 23% of everything there is to do.