The idea is fun, and seeing rats moving around everywhere sure is amusing.
However, I do think it's a shame that most of the controls aren't required to complete the game (only the left click to move the rats is useful). Maybe adding a limit to mice by cage and having cages of different scales could help (to force the player to both scale the rats and yourself).
Appart from that, you went crazy with the gun VFX I like that haha