A button to restart would be great! Good concept, mildly annoying execution since I found not all of the enemies to be reachable, even with the bullet attack. Some parts of the level if you fall down, you can't get back up, making it unwinnable. This by itself is not a problem, except you can't press a key to restart the current level! Doing attacks despite being dead was amusing though.
Sidenote: The two enemies at the end of the first level, I thought there was friendly fire or something since one of them had disappeared when I checked on the group later. I guess they were both in the same position? Not a major deal, just food for thought for a different game idea.