I like the art style - it is charming. The simplicity fits the story. One note - the menus' background is too precise compared to the rest of the game. It is more fitting for some engineering game.
The whack-a-mouse is cool. Sneaking was challenging - I think I counted 4000 miliseconds between the human's appearances - it may be good to keep it a constant time. Looking forward to drowning that metal toy!
Another suggestion - you can make the bush where the mouse is random. This would increase the replayability.
Great game!