I like a lot how the theme is applied and I'm impressed by the variety of items, different attacks and enemies. The main attack feels a bit slow and and makes the first moments of the game a bit boring, but it changes once you pick the first item.
I think I miss something to complement the unstability mechanic and make it even more meaningful. For example, some POI always shown on the map would make me think how to use the time I have left before this level falls.
Anyways, I'm impressed of what you have achieved and it's a very good game!
-Aleix