The coolest part of the demo was how things looked while UNDER the water. Most games don't even let you go underwater, and of the few that do, they usually just tack a grayish-blue filter on the screen and call it a day.
Uncharted 1's best tricks were its animations and surface water. Uncharted 2 built on that with snow and set pieces that collapse all around you. Uncharted 3 is bringing to the table sand, underwater graphics, and changing set pieces that involve water. It seems like a pretty typical leap for the series.
At this point, they're not going to tap anymore power out of the system. It's just a matter of enabling their engine to do things with that power that it couldn't do before (ie snow in once scene, torrential flooding in the next). You shouldn't expect much of a leap in polygons or textures past the first few years for any capable developer.







