Personally, I thought it looked great. The graphics looked much better, although it still looks like the original copy of Halo 3. The lighting was much better, and the textures were much sharper. But I'm more looking forward to playing this co-op, and the 3 new maps that come with it for Halo 3 multiplayer.
The Halo:Reach beta is just an added bonus to a good expansion with 3 new maps for Halo 3 multiplayer.