I played it with the DX11 patch on a Q9450, GeForce GTX 460 in the resolution 1680*1050 and got a very fluid framerate. I think the graphical difference is pretty small. I don't think the patch actually changes lighting but just adds a bit of tesselation.
I'm also with the Crysis > Crysis 2 crowd. I really liked the quasi-sandbox (because it was still pretty linear, it just hid it) where you could hide in the bushes, scout the area extensively and then plan your approach and escape. Together with the solid physics system this meant a lot of options.
In Crysis 2 I couldn't even smash in a window because the designers thought I should use the already broken one next to it. Really annoying were the corridor levels though. You would walk through a corridor into an open field and have to leave through another corridor. The entry point didn't allow to move around in a safe distance but instead always threw you right in the action where a few steps in you would be under fire already.
I played both games on the hardest difficulty so this might influence my experience.