Nice pics! I like the Sniper. He looks badass.
For the Pyro, it's hard to see the silhouette of the legs. Your artwork should probably pay more attention to the always important shape and silhouette of the characters. I dunno about the Heavy and Scout pic, though, I think the poses are weird for this kind of art.
EDIT: About what Fearlezz said - I will just assume you haven't just put on a filter, although I can't be sure since I lack any sort of knowledge about image editing software.