The gameplay was good and the grades were good as well, but the Mech upgrade that makes it so you can shoot from front and back makes it extremely difficult not to destroy the factory and to get the good ending. In a way, this makes it unfair and when you compare it to the story, will either mean you shot from the factory entrance and let the robots destroy it or you moved around and ultimately destroyed the base yourself. I'd suggest making it so the player's bullets can't destroy blocks. Also, for the mech upgrade (the upgrade where the entire appearance of the mech changes), Perhaps you should have an indicator for which mech has already been bought.
The only only thing I can suggest is a level selection screen of some kind or being able to replay the last level after beating it because as much as I enjoyed playing this, I don't want to go through it again to get the best ending medals and I like medals. Still, very good job.