I love the concept! But I think it gets a bit boring when you can just do the same strategy with the same box that keeps regenerating every time. I think it would be more interesting if each character had a different ability, and the game built up to having so many character rotations level by level (you start with one, then add another with a different ability, then a third with a different ability, etc...) For me, this would have made more puzzl-y and engaging.
Great graphics and sound effects, and great concept :)