This is an incredible game! Everything fits so well together, if this doesn't make it into Mark's video I'm going to be really upset!
If you wanted to continue building, more level variety in terms of tile set would be nice. As much as I like infinitely cleaning the floor with ninja some additional areas could be nice. Adding an overarching story and a reward for no errors would be nice too. I feel like this game has a lot of speed run potential too.
Overall fantastic game! I can't wait to see if you do anything more with it. Good luck on your future game dev journey!