Hey. I have a few suggestions for this game.
I think the key combination that you should use, as most people are familiar with it and expect it, is either arrow keys for movement, or WASD for movement. W=up, S=down, D=right, A=left.
When I played it, there weren't any enemies to shoot at, it would be nice to have some, in case there aren't any.
Also, the bullet speed should be much faster, and it should be be released instantly after clicking.