Really fun game. It's challenging, but it is never frustrating. When you start off the game it is relatively easy, however after a bit it starts to get hard. The root of the difficulty does not come from the gameplay mechanics (which are simple and easy to learn), but rather in finding a consistent strategy for beating bosses. This causes the game to not get monotonous. Also, the presentation of the game is stunning. The music creates a looming sense of tension, but still manages to be great from a compositional standpoint. However, the only real criticism I have of the game is the visuals sometimes hinder you unintentionally. This is demonstrated well in the flying levels, for example, something will in the foreground blocking your character or the enemies' attacks. Other than that the game looks beautiful, the art style encapsulates what it is trying to portray very well. The animations are vivid and the bosses and stages are so unique and distinct from one another. This isn't a criticism, but rather a tip: Play this game with a controller because the keyboard controls are inconvenient and don't work for a game like this.