This is not a great game (yet) but it has the potential to be.
First of all, I really like the graphics in this game, and the attention to detail as well. Definitely one of the best games in terms of graphics in this genre.
I encourage you to make an update or a sequel. I know that you have spent 7 years in developing this game, but I believe you have taken care of the hardest part of the code (the basic engine, the graphics, enemy movements etc.).
All the tweaks you need for this game should be relatively easy to code. These include ammo limit / reload mechanics and an actual story etc.