Yes, I specified PC for a reason. The X-Box one is the most often discussed and indeed PC is largely the same save a few things...
The Flamethrower. Seriously. I love this thing. It sprays out at medium range which isn't as good as other weapons, but those flames STICK. Even a short burst will cling and burn off someone's shields and kill them no matter how fast they can run.
Fuel Rod Guns. And here you were jealous because only the Hunters could use them before. Not as well-ranged as the rocket launcher, but they're great for bombing people you otherwise can't reach without exposing yourself.
The Bison. Okay, it's a name made up by me. The warthog is a bulky yet maneuverable vehicle with decent firepower in a machine gun. The Bison is a bulky yet maneuverable vehicle with a frightening amount of firepower in an onboard tank gun that unlike the scorpion; can let off three shots before reloading. Oh, and it's black. That alone is awesome.
Banshees. Oh. Hell. Yes. You use them briefly (one level is it?) in the single player game, but come multiplayer; they're yours for the picking. They may not be as fast as a warthog or ghost, but the front-mounted fuel rod gun gives you good bombing power, and their front lasers pack more punch than your average ghost. Oh, and they fly. Not hover two feet off the ground and crash when they hit even a small hill. FLY.
*More Maps*
Death Island, Infinity, PC Multiplayer's added perhaps more than half a dozen new maps not previously seen in the X-Box edition. Some are generally meh, but others can likely rate as the most fun since Blood Gulch.