As I said before the biggest difference is really just the fact that you get to play with other people. The game play is practically identical to the original game, with all the parachuting, grappling and car surfing all working in the exact same way.
All my fantasies of having extreme bus races with another person were realised, and more. So everyone was delighted and surprised when it actually happened. The idea of surfing planes into the ocean with a friend was just an awesome thing to imagine.
I think all people who played Just Cause 2 had fantasies of a multiplayer mode being made.
