A buddy of mine wrote an Xbox 360 review. I'd concur with his points, though I'm curious why he is setting up Windows Media Connect, as I thought the Media PC itself was enough.
I'd also like to stress the coolness of the Achievements. Yes, you get to see how your friends are doing, but you also get to lord it over them when you're kicking their ass in gamerpoints. (yeah, I'm looking at you, Chip... hehe...) It introduces a nice amount of friendly competition beyond the gameplay experience.