The movment system is quite fun, and you know its good when you get the sticky keys...
I think only having the boss be attacked when it is green makes the game feel alot less methodical and fun, ussualy you have to worry on how to not take damage but also do damage, here you just have to do 1 or the other which makes the game less fun than it could be :/.
The art is really good and the boss design is nice, with the turret coming out of his back.
Only criticism art wise is when the boss is rotating, the particles should not rotate with him. Not sure which engine this was made in but in unity it would be world space to make the particles not follow the transform of the boss, that simple change would be a cherry on top. The players spinning particles look amazing !
Great game, good job ! :D