Low polygon count? I don't see that. The reason Crysis rips most graphics cards to pieces is because of its high polygon count. The games look pretty similar as far as detail rendering.
I don't own a PS3 and haven'tseen Uncharted 2 in person but comparing videos of the two games side by side, Uncharted 2 looks really good but has a "plastic" look in my opinion. Maybe that's Youtube. Crysis has a natural look without the CG plastic texture and the movement of people in Crysis looks more natural. Just my opinion.