Nobody yet knows but the feeling is if you can run original Crysis then you should be able to run Crysis 2 better. In my view if the game can run on the consoles then any half-decent PC should have no problems with it.
I would guess atleast a dual core + CPU x3 for amd cpu's. Also 2+gb system memory, a nvidia 8800+ or ati 3870+. now I would guess these as the recommended requirements. Now for maximum requirements 8 core CPU, nvidia 600+ ati 7000+ in tri sli/crossfire, 6+ gb ddr4 ram, and an ssd
Crysis 2 what people have not realised will have better textures and more graphical features but will run the same because it takes alot to run all that grass not to mention plants and in the city there is not much of that so it will run better EXCEPT there is a flooded central park level that has tons of grass and trees