This game's a masterpiece and I adore it. I love shmups to bits, and from a pure action/aesthetic standpoint the game totally rules as a shmup. But what really puts it over the top for me is the storytelling -- the game has some super-clever structural quirks that help it build to a moving and unforgettable finale. I've seen a lot of folks compare it to NIER and Undertale; I love those games and I think the comparison's very appropriate.

The only other shmups I can think of that approach this kind of storytelling are Hellsinker and Siter Skain's RefleX, some of my favorite games ever. If you like those games deffo give this one a look, and vice versa.

Highest possible recommendation.