Absolutely lovely! I can't imagina the amount of work this must have been. Really fun, with an also fun art style.
Two small suggestions:
Making the cat speed faster/slower depending on the mouse distance could be a nice idea to allow finer movements. Moving the camera a bit toward where the cat is moving could also be nice, so when we walk 'long distances' the cat is not close to the edge of the camera.
But these things absolutely did not get in the way when playing. A really nice piece of work!