I really enjoy the style of the game, it fits the theme very well. I enjoyed the out of control nature of the gravity. It flips often enough to keep the game enjoyable. I also really like that you have a two player mode, it adds a lot to the game! I also like that the main menu functions as the tutorial, that is very clever!
I had some slight problems with the doors being open and actually registering that I am in it. It would be nice to see it fixed in a future build.
If you wanted to keep building, additional objects that are impacted by the games gravity would be fun for puzzles, or even gravity flipping multiple ways such as to the sides.
Overall fun game! Good luck on your future game dev projects!