HAhhhhhhh what?

I think it's great, the light source doesn't bother me one bit. People might think that you need one main lightsource, but in reality light reflects off surfaces and you can get more than source. I would take what someone tells you here on DA with a grain of salt.

If I had to guess, I'd say the lighting looks like it's coming from just behind mostly, and that's a great effect, the overall image is dark and fits in well with a dark mood... back lighting adds a mysterious affect. You've used contrast and enhanced the parts that should show up the most (around the face), and you were subtle with the rest which is perfect, , ... it's all about casting atmosphere and mood and establishing a focal point and you've accomplished that wonderfully. I wouldn't change a thing.

And about his nose being flat.. well... I mean.. let me introduce you to Deadpool loki, he's rarely drawn with a nose if he's got the mask on. Or if they do throw in a nose when he's got his mask, it's a hint of one, very flat in most depictions.. X Force or otherwise. Actually fully sculpting out a nose on this guys face would be as strange as sculpting out a full mouth behind that fabric and it wouldn't make sense.