This is pretty good. It may be two disparate genres duct taped together (think: Catherine), but both halves are well done, there's more to it than just gimmick.
First it isn't actually a visual novel, at least not in the sense that Japanese players use that term. VN's don't really have gameplay to speak of, this is much more of a puzzle-adventure, where you work through a series of trials. It's kind of Danganronpa meets Phoenix Wright, with a little Squid Game, it's not bad.
The shmup sections are excellent, and they're developed by G.rev, who are one of the best shmup devs around. In the game itself, these feel a little easy because they throw a million lives at you and they throw in dialog puzzles in the middle, but there is a pure shmup mode you unlock as you beat each chapter, and this strips out the other stuff and lets you play it proper arcade style.
This "score attack" mode is enough to stand on its own, and there are a ton of stages, all with their own bosses and even online leaderboards. It's a full fledged shmup with a combo based scoring system and some meat on its bones. But of course you need to play through the game to unlock it all so don't think you can ignore the other half.