you won't get any good answers out of the types of people who post on /bant/ these days, I'm sorry
They can be fun games if you think you would like difficult, fast-paced shmups, and they have a nice aesthetic with cute girls. If you don't enjoy the games you can always just read the doujins.
Most people recommend starting with Embodiment of Scarlet Devil, which is the sixth game in the series and the first released on Windows, but I'm sure you can start with any of them have fun, since you don't need to follow the continuous story.
