I think the models are ok, I do like the gun model.
also what you could add in the future, this is only my opinion, but shooting events. like if you aim at the head, you get a reaction from the head, or legs he falls down a little.
on the models what you should do is practice more, and learn from tutorials, try Grimbers low poly model tutorial for a start then go to more harder tutorials. I used that to help me with my models, even though I can't saay my models are perfect lol
in time you will get better, it feels better to do your own model.
I really like the idea of the crosshair.