Lighting got gimped.
Either way, its really impressive. I saw a comment somewhere that i think sums it up. I think in some respects, it looks better than pc, in other respects i think the pc looks better. The trick is to hide, what they scaled down, with what they have visually changed and improved. Like the guard in the jail has chain armor around the arms now. To me its not necessarily higher res, but it catches the eye differently and thats what makes it look better.
However on High, or with Ubersampling on, i dont think the 360 stands a chance.