Personally, I was never a big fan of the bump-mapping in Halo 2. I didn't think they looked as good as in Halo 1. I did like the bloom effect though, and that environments were much more detailed.

I think that the HUD looks good. I do think they will change the vertical grenade numbering though, it doesn't look quite right the way it is currently. It's not easy to see the number at a glance, especially when it's showing 1 nade.