Excellent!
Now this was very impressive. Right from the beginning I was impressed by the simplicity of the controls, the graphical style, and the choice of music for each situation.
I'm not going to lie, this isn't exactly the most deep, complex, or even long game I've ever played - but it never claimed to be any of those. For what it is (boss fights) I think it delivers superbly well, and in all honesty I could not find fault with it other than it ran a little slowly at some points (but that is almost certainly down to my computer more than the game itself), and that it is a little too easy - to those who think it is too hard, as has been said, man up! The defuse puzzles are incredibly easy, and the bosses themselves are not hugely difficult once you have the hang of them.
My favourite touch was the first boss in the game, as I felt he had a little bit more character than the others, given his animations, and quite baffling final form that I could not help but laugh aloud at!
Author, I implore you to please ignore the mass of strange individuals who have marked this low and made uninformed, rude comments about it, because you have done yourself credit with it. If you ever make a 'full' game, then based on what I have seen here, I would be very excited to play it.
Well done!