Amazing concept, reminds me very much of The Lost Vikings, and the additional twist of fusing the robots for additional abilities makes it very interesting.
Unfortunately I got stuck at the laser from the ceiling and couldn't figure out how to go forward; fusing the green and blue bot allows those two to pass the laser, but the red one was always left behind and got killed. Not sure if I missed something, or if it's a bug/incomplete feature.
In short, very nice concept, with some work on the ui/controls side, it could be a very nice game!