I could not believe it, until I observed my system via HWMonitor. In fact, crysis 2 caused my graphics card to overheat. The result was a jerky gameplay for ~30 seconds about 4 fps, while it ran @ 30-45 fps the first 10-15 minutes.
Due to overheat protection the graphics card slowed itself massively down for ~ 30 seconds.
Never had such problem even with high detailed and complex Shooters or RPG.
Somewhere I found a useful hint, which has solved this issue for me. I created a file "autoexec.cfg" in the crysis2 main folder with just the line "sys_MaxFps=25" (without quotation). By limiting the max fps, now my graphics card is no longer overheating, and gameplay is smooth all the time.
Oh, you can also set the max fps (and much more) with the program "Crysis2AdvancedGraphicsOptions1_7".
Hope this helps.