Shmups are the genre I've tried the hardest to get into only to give up.
I tried a shitload of shmups, several Touhou games, Batsugun, Dodonpachi, Mushihimesama, Ketsui, Deathsmiles, you name it and I quickly got fed up with every single one.
Shmup players are always saying how great these games are, and sure, I can see the production values especially in the arcade titles, but shmups just don't have enough stuff you can do, like enough moves. Your only interaction for most of the game is moving in a 2d plane and even shooting is kind of superfluous since there is rarely any reason to not be shooting. Games like Dodonpachi are treated as revolutionary for having a mindblowing two fire modes instead of one. I don't know, it's just too much investment required for too little meat in what you can do with your little ship.
For comparison I like games like Nioh where you have a shitload of moves and a lot of room for creativity and style in how you play the game.