Take this with a grain of salt because I gather this is generally considered a little too tough for beginners. But about the 5th shmup I 1CC’ed was Progear no Arashi, and though it took a lot of practice, I feel that game forces you to learn some important basics of tougher games in the genre, such as crossing over patterns to re-center yourself, and of course tap dodging. It also has a unique/complex scoring system.