Just purchased the game and with only an hour of Game play I can say it is by far the best game I have ever played!
I haven't had the chance to play the online, but from what I've read it is really fun... it has everything the normal game has except the story... you can go around and make havok all around the city... I'm probably going to try and beat at least half of the game's main story before heading online... I don't want to get too distracted! It really is pretty hard to go a stray though because of the story... the characters bring the game alive... Seriously, if the game cost 120 bucks I probably would of payed it! Thats how good the game is!