Haha. Great idea to only let the player move on the walls. Also quite a clever solution to remove the fire button and just spawn projectiles when bumbing into "walls". Art and sound are great as well.
There are just a couple of missed opportunities in my opinion: Being able to walk through doors when they are closed for example (and only when they're closed of course). And the vacuums take away a bit too much control in an already very confined space in my opinion. In general I wonder if there are enemy types that support the very confined space you're in a bit better... Not a super big deal, though. You got around that problem by making the walls a bit thicker here and there. :D
Your game has a good length and difficulty for a jam game in my opinion. Overall very well done and enjoyable to play. Nice, nice. :)