Very brave submitting three minutes before the deadline ;)
It was a neat idea, though the gravity flipping mechanic ended up not having much presence in my gameplay. It seemed like both the top and bottom papers spawned the same set of enemies, and I setup my towers to basically mirror eachother on both the top and the bottom, so I had no reason to use it. I made it to wave 12 before feeling like I was going infinite, and I didn't know if there was a target wave to hit before the game was over, so I quit at that point.
I did like the game, though! The tech for this feels pretty impressive given it was made in such a short amount of time and the audio/visual FX are good.