don't play ikaruga. it's very pretty and people who can play it competently are brain geniouses but it does not really prepare you for the vast majority of shmup mechanics, and the additional layer of complication that the polarity-switching adds on top of Just Dodging Shots is actively harmful to someone trying to learn their way around the genre. you would be much better off playing ANYTHING by compile
You can play M.U.S.H.A. on Switch right now if you have Switch Online with Genesis games! Go try it.
the only shmup with a giant lesbian mural in the bath level