Just got that issue this week. The game looks really sick--dynamic weather, normal mapping, some Ubisoft fashioned "spectral" highlighting. Really crazy. The Xbox pics look extremely close to the PC shots (most obvious difference is the resolution).
Gameplay-wise, the biggest addition is the open-level structure which eliminates the trial and error style that so many peeps here tend to hate.
Edit:
There are tons of little things that the game is adding that are just icing on the cake. Sam has that new knife he wields now--he can use that to cut holes in stuff etc. Also, the sound is getting a complete rehaul and is supposedly one of the most advanced models ever made. Rain gathers and bogs down Sam the more he is in a downpour. Some of the Spy co-op shots are great as well...