Nice game! The feeling of being overrun by monsters is very creepy, even without sound, and I love that they're just small enough to be hard enough to hit, adding just the right amount of challenge for aiming with them. Love the lighting effect, it really made the start spooky when I couldn't properly see the monsters when they first entered the room.
In your screenshot it shows you standing on the top floor. I wasn't able to jump that high so I had to stay on the middle floor until I fell to the bottom, at which point I couldn't get back up to the middle floor.
The full on assault starts really quickly, making me feel overwhelmed and hopeless before I've even dealt with the monsters much. I would probably slow the spawn rate down a lot more at first. Giving the player the chance to deal with one monster at a time for a little bit, then gradually some more, until finally they're overwhelmed.