Thanks a ton for trying it out!
The controls are below (as copied from my game page):
Move around with A D, shoot with the Left Mouse Button, and slow down time with Shift. You can swap bullets with the mouse wheel. You can Interact and Reload with R when prompted. You can also Pause with Enter when in gameplay and hold Escape while paused quit.
As mentioned, you can only damage enemies when they're in the air. That's the gimmick of the game. You also get powerups by clearing out rooms which changes how your gun works.
The title screen also shows you the controls (that's what the blackboards are for on the title screen), but I suppose those could've been more obvious and in detail.