MGS4 graphics are nothing special. The game has no draw distance what so ever and frame rate stutters like its drunk. Now Squil reveled it runs on a low res too...
If you are talking about movies...then yeah...MGS4 looks nice when playing the 12 hours of cinematics.
Maybe you don't like Halo's 3 art style and that is perfectly fine. But as a technical achievement...Halo 3 > MGS4 when it comes to visuals.
(Draw distance, lighting, frame rate are all superior...and even supports split screen)