The art and animation are simply amazing. Incredibly well-polished and professional. Possibly best-in-show in that regard. Kudos to the artist.
That said, the first boss was simply too challenging and I felt the game was just too punishing in general. I gave it many attempts over about 30 mins but could only get to the part where he starts throwing the more frequent but narrower beams. I think it would help if there was a sense of progression to the boss fight, to show how much more dodging you have to do before it ends—but without knowing that, I just wasn't willing to see it to the end after sinking in so much time on just the first boss. I think if the movement and controls were a little bit more fluid, keeping it at the current difficulty level might work, but as is, the beams should be less frequent or not last as long, or maybe start the player off with more life.