I liked this concept, thought the ability to control four characters at the same time was really good but the fifth level was very difficult and took several attempts until I managed it.
I think this is worth taking further, you should consider what you could do to make this work for a longer project and how you could change the gameplay to keep it engaging for the player. Perhaps adding some element of power ups that when collected by one character would temporarily stop another to give you time to get a character into place. Just a random thought but it might mix up the mechanics a little after you give the player enough time to understand how the basic functionality works of course.