That final boss took years off my life, I was clenched up for that entire final phase and I can't even describe the sense of release I felt when I finally beat it. That's the sign of a fantastically designed boss right there, and really just a testament to how fun this game is from start to finish. I love how much it pushes the player to strive for perfection, every mechanic pushes the player to not make a single mistake, to the point where there isn't even any immunity after getting hit which I'm actually a massive fan of. I do have one qualm though, which is how it feels to hold the fire button, it took me about 10 minutes to beat that final boss, and throughout that time I had my hand held on the K button for 90% of it and it started to feel genuinely uncomfortable. I'm always of the opinion that if something requires constant holding or mashing in an action game then it should probably automatic. Either that or pressing K toggles fire on or off, that way you can still have the multi-tasking of having to turn off fire to spin.
That aside though this game is BRILLIANT