I love the idea and the way the map is so colorful at the end. It would be great if you can implement some kind of "final rewind" where you get to see all your little guys been turned into a color stain at the same time.
The gameplay feels really nice when you can get quickly to the unexplored areas but there are some levels where the position and speed of the enemies make it very tedious to repeat the known part. Maybe you can try the idea of doing some levels with only static - predicticable enemies.