Some of the multiplayer changes are questionable. They are instituting a CoD-like loadouts system where you get to customize weapons and armor abilities you spawn with; also, all on-map weapons will be randomly spawned a la the ordinance drops from Reach's Firefight mode. One thing I always liked about Halo's multiplayer was that everybody spawned with the same weapons (though in Reach you could change weapons and armor abilities depending on the game mode, but that was reasonably well-balanced) and so anybody who performed well did so based purely on skill. Now, we'll have all kinds of people spawning with noob tubes (or the Halo equivalent thereof) and the game will largely lose its more skill-oriented approach to performing well.
However, I, too, am largely in it for the single player, and I gotta say, that music sample sounded pretty good. Not Marty O'Donnell's work, but it did certainly still sound like Halo. I'm looking forward to the campaign; Reach was the first campaign to even compare to Halo 1's, but I'm looking forward to (once again) being stranded on a strange alien world and getting to explore new places.