Shmups, I'm only a beginner but I have a few suggestions:
ESP Ra.De. - somewhat slower bullet hell with pretty interesting scoring, the "Psi" re-release has a lot of useful QoL features.
Espgaluda II - you could think of it as a successor to the former, it has refined gameplay and recent releases have great QoL features. Somewhat faster paced bullet hell?
Ikaruga / Radiant Silvergun - Although these are two very different games, they have entirely different mechanisms to most other shmups. Ikaruga feels like a "puzzle" game a lot of the time, while Radiant Silvergun has some light RPG elements. Both are somewhat hard to get into imo.
Dodonpachi Resurrection - great starting point re bullet hells, the recent re-release offers a ton of QoL features and the game itself has interesting scoring / gameplay. Soundtrack is awesome.
Raiden IV - Super biased, but I love the soundstrack. Pretty great, if simple, game otherwise.
I have many more shmups in my backlog (Ketsui, Dodonpachi Daioujou, Battle Garegga, Rolling Gunner, etc) which I'm sure I could recommend, but seeing as I haven't played them first hand yet... I'll leave it there for now.