Honestly I am not sure what I expected, but surely not a boss fight of really enormous proportions! Design of attack and theme are amazing and it all comes together so well with that epic soundtrack! And also voice acting? Top notch. Really well done.
If I had to add some criticism though, that would be telegraphing of barrel attacks. Every other attack is telegraphed beautifully, from drills getting stuck in the floor to paint preparing to explode, but the barrels did get me completely out of the blue a couple of times. Other than that, truly magnificent.