You definitely have a lot of potential here. Considering this is most likely one of your first few submissions (I haven't seen you on Newgrounds before), this is really a good job. I must criticize because I believe it will help you out. I am not really an animator myself, although I would love to be, so please excuse me if you thing I am being to harsh.
Firstly, I think you definitely could improve the atmosphere. Maybe take a look Xionic Madness to kind of understand where I'm getting at. It was a shootout, but I really didn't feel danger. Maybe the music choice, but I think the animation could have been faster paced. Once again, I understand you have not yet mastered this yet, but implementing the camera shakes during the fighting is something you should use in the future.
Another good thing is that sound effects could definitely be amplified. It adds tension or excitement. You could also improve on profile shots and distance conception.
Once again, I am in no way attempting to make you get down on yourself, this is merely constructive. I hope you strive to improve and make a name for yourself on Newgrounds!