Well,first reduce shaders quality to low settings.Theres no difference between low and ultra in shaders quality except for SSDO(Screen space directional oclussion) which is very taxing on the system.Next increase object detail to extreme and if that takes up too much performance then lower it to very high.If you have performance to spare increase post processing to Extreme,AS THIS SETTING will give you near max image quality so try and keep it on extreme and reduce all the others to low.
If you are into advanced tweaking of crysis 2 like I am,then this tweak guide should help you get the performance and Image quality balance.
http://segmentnext.com/2011/03/24/crysis-2-tweak-guide-graphics-and-performance/
Remember to keep every setting on low settings (high settings in game) BUT object detail on extreme,and if you have the performance to spare turn post processing to extreme.