I've played a lot of Halo 4. Not nearly enough, but enough to get a picture of the game. With that, I realized something. The art in Halo 4 is fantastic!
I can honestly say that I think on most websites and magazines, Halo 4 will win the "Best Art" category. Even the multiplayer maps have perfect finishes on them, and it makes them even more fun to play.
And Halo has always had great skyboxes, but I think that this one takes the cake. It has made exploring the world much more enjoyable, at least for me.