MaxMultisamples=8 (improves AA if it's on, you can also turn AA setting off in game and force through nhancer\ccc it manually for better quality, but it's buggy for now)
MinShadowResolution=256
MaxShadowResolution=2048
ShadowFadeResolution=512 (Improves static and dynamic shadows)
bEnableVSMShadows=True (improves dynamic shadows)
You can also experiment with these lines
MaxDynamicChunkCount=1000 (number of debris pieces lying around)