As a sim, it does suck, but I dont think of it like that. For me its a game where i can just cruise about (more like boot it) and, when Im online, go on hugely long tours of the island with random people.
As a racing sim, it sucks, as a fun driving game, it is a good game.
Oh, and the motorbikes handle like shit. sensativity all the way up helps a little, but not that much.