An interesting idea. The bosses are challenging and have distctintive attacks, although I feel that in some difficulties they can be a little bit relentless. I love that you can custom your own Metal Top Solid, that's a cool feature!.
Overall, I had a great time, good job!.
The only thing I would change is the way you attack . Clashing with the bosses like a Beyblade would have been more fun that just shoot at them.