From IGN for those interested:

http://xbox.ign.com/articles/666/666049p1.html

9.5 Presentation
Subtle, minimalist HUD, menus, and interfaces. It's all about believability, and Valve does it better than anyone.

9.0 Graphics
Excellent for the Xbox. This isn't high-end, high-resolution PC imagery, but the graphics are nonetheless damn good.

9.5 Sound
Great voice acting plus superb music equals top-notch sound all around.

10 Gameplay
A huge variety of missions, experiences, and suprises will have you riveted all the way to the end.

8.5 Lasting Appeal
A 16- to 18-hour single-player game with tons of little things that are worth going back and finding. The G-Man awaits your search.

9.4
Outstanding OVERALL
(out of 10 / not an average)