Bungie has stressed that the beta is only an early preview of the game, which means that the development team is still working on the graphics and gameplay elements. That didn't stop Gamespot from taking a few screenshots to see how the current graphics compare to Halo 2, but please keep in mind that these shots of the beta do not reflect the final game.
In the article, the default images are Halo 2 unless otherwise stated. Mouse over each image to see the Halo 3 comparison or alternate view shot. Gamespot maintained a widescreen aspect ratio for the cropped Halo 2 shots, but they had to revert to the 4:3 aspect ratio for their full-screen Halo 2 images because running the game at 720p on the Xbox 360 only produced a stretched out image.