I know that Crytek had all graphical bells and whistles in Crysis 2. Even exclusives like KZ3 don't have SSAO or HDR for example. Yes, its more polished and yes it smoother,also native 720p but there are things they cut out. Its all about compromises and Crytek went for frame rate in C2.
Just the first level, when you get out of the gate and you get almost a forest in front of you. I guess those trees are very hard to render since there is alot of them, there is more polygons and alot of them cast a shadows which, because of threes swaying in the wind, play around in real time. Its much more open than any other shooter with those graphics so pop up is expected. I know that was one of the levels frame rate dragged down. Some other graphically heavy games carefully avoid these kind of tasks, but I guess Crytek couldn't because of their vision and PC version which would then seriously suffer.