New guns, new enemies, new heroes. Life and death.
The controls are different, but after getting used to it, I'd never switch back. Love the graphics, Bungie really did a good job on this one, as they said, they had a totally different graphics predecessor. The story mode was well thought out and was a good length campaign.
A lot of people, I've noticed didn't like the fact that the original hero, Master Chief (John-117) wasn't in the plot. I really liked getting away, a relief from watching the annoying Cortana get tortured (You gotta admit that was cheesy) and no more listening to Cortana telling me what to do. Yes I had a few complaints about the first halos with Cortana, but I still liked the game play.
The multilayer is amazing with very few glitches, and if you can find an armor ability that suits your needs, (Mine is the jet pack), you're good to go. A lot of people complain about the armor abilities, but I'm totally fine with it. If you can find one that suits you, I'm sure you'll be fine with it, too.