I really enjoyed. Apart from the controls and art style which is great I see many great details. For example, the robot loosing one arm/weapon when is low in health or the transition scaling the minions when appear. This kind of details helps to have an overall good feeling when someone play. If you have time, add some ambient sound mixing boxing and robot sounds. Perhaps you could find an audio of a robotfight that would feet perfectly.
Congrats for the game.