Solid idea! I really enjoyed levels 1-3. The game concept was creative and also played well.
Level 3 felt quite long to me - the patterns were interesting and well-implemented, but the first half where the attacks are slower tested my patience. However, the final few patterns and especially the ultimate attack were enjoyable to plan around!
I was thinking that it may be fun to have another attack mechanic, so when I arrived at level 4, I was pretty excited. But there were a few things that ended up bugging me:
When one character (1) picks up the other character (2) while 1 is standing on 2, he is rendered immobile and you have no choice but to throw 2 in place. Also, many times when I threw a character at the boss, 2 would immediately stand on 1's head, and no damage was dealt to the boss. It felt somewhat random and finicky.
Also, I didn't really get what was going on with the lasers. That's probably my bad, as I didn't pay as much attention to the dialogue as I should have.
However, that was only a small segment, and it didn't cause me to enjoy the earlier parts any less! I enjoyed the switch mechanic as it was seamless and allowed for quick and deliberate play. Great stuff.