If Uncharted 3 is as much of an overall improvement visually over Uncharted 2 as U2 was over the first, I'll be truly amazed.
Uncharted 2 still boasts the best console graphics to date IMO, and that's saying something as there's a lot of great looking games out there. God of War 3, for example, has excellent character models and detail, but overall it's just not as much of a treat for your eyes to watch the game in motion as you play. When you consider how smooth it runs, texture detail, animation; I think Uncharted 2 is still king.