Looking at videos , i've seen an annoying thing :

When you shoot with shotgun , there is a quick light that appera disappear :
It is disturbing and annoying when you are shooting a lot : it looks like some storm
When you are hit by zombies , same thing.

Why not using a more subtule lighting effect (and smoother even if quick) ?
Same thing when you are hit, use smoother full screen effect
with fast smmoth appear/disappear and red screen would be better like in COD4 !