I'm terrible at perspective, so I'm reluctant to redline on that. What I notice is that the Sniper's proportions are way off even considering the odd angle. GIS the phrase "sniper huntsman" and you'll quickly see what I'm talking about.

I'm afraid this is not the best redline-esque thing in the world. I can only really help with the face because I hate perspective with the burning passion of a thousand binary stars.
Anyway.
Hi! Nice to see some new art posted here! In regards to your face you have a good grasp of expression - I like his sneer, the squint of his eye - not to mention the crow's foot is a really nice touch.
His eyebrows are too arched and/or thin. Sniper's eyebrows are quite straight, heavy and forward. I find it hard to see his brows in this picture, which can be a little odd. Don't be afraid to beef them up a bit!
His nostril is too prominent. I say that because I feel his nose should be angled down, but at the same time it looks to be viewed from the side. In reality his nostrils would not really be that visible from a downward angle.
His sunglasses are possibly the main reason why his face looks a little skewiff. His sunglasses are at a different angle to his face. I find it hard to explain but hopefully you can see what I mean in the redline.
I feel his hairline is probably a little too low. With the possible exception to Scout, the rest of the team has a case of receding hairline going on.
Those are my main points to make in regards to his face. My best piece of I advice I can give is to simply use a reference! If you go over to the Resources thread here on TF2Chan there's a whopping great big thread (the first one, I think) full of renders of all the classes. Pay particular attention to their jaws, because pretty much everyone has a Manly Jaw of Manliness.
I hope this is of use to you. This is the first time I've given advice in donkey's years. But please keep drawing! You can only improve from hereon!

I can't anatomy, but it looks to me like Sniper should be aiming for the lower-left, but the arrow seems to be raised up a little from where his left hand is, and pointed more down the center. Like, it's not touching anything other than the hand that's holding it, and the tip is just kinda floating there. Which I suppose isn't impossible to hold it like that, but he sure wouldn't hit anything he was trying to aim at like that. If I had to guess based on Sniper's posture, I'd say the arrow should be pointing roughly to the bottom-left corner, maybe even cut off at the end. Based on the arrow's position, I'd say Sniper needs to be facing the "camera" more like the arrow is.

Hope I could help.