Oh man, it's a pity you played it minutes before I uploaded an update with a new enemy. Getting stuck probably happens because you click outside the screen, game loses focus, then you release the movement key, click back, and the game thinks that the movement key is still held. I'm gonna do something about it, yes.
Also, you don't need to keep clicking, you can just hold LMB, and the gun will shoot as quickly as it can.
Anyway, thanks for the feedback!