Couple of things:
1) I'm of the opinion that there's a bit too much artistic license when it comes to the lighting. (But then, I'm a huge lighting nerd and I love diffused light through a window, so.)
2) This looks like a dude in a costume, a prop owl, and a prop gun, not the Sniper. Included in my redlines are references for the Sniper in profile (it looks like you gave him a mullet, so I went to the wiki and grabbed a screenshot of Your Worst Nightmare), the relative size of the rifle to Sniper and how he holds it, and of Owliscious.
3) On that note, Sniper's missing a lot of crucial details that help us identify him: his underbite, his head profile, his one glove on his left hand (lefty Snipers have the glove on the right hand), the little window on said glove, the piss-colored glasses, etc. These are things that should be faithful to the original regardless of style.
4) Snipers arms lack proper musculature and the placement of the elbow seems too high in relation to his arm (this may be because the lighting has obscured where his elbow is). The place where his sleeves are rolled up also conflict slightly with the angle of the arm (unless, again, there's something going on with an unseen armpit, but in my opinion there's not enough visual information there for me to conclude that).