Something I've been thinking about today ever since
@Dom Cruise mentioned it in an entirely different thread are those anime series that are pretty obscure nowadays but were popular at a specific point in time to a specific age group.
What I'm talking about isn't just anime that was really popular but then faded in popularity but is still well remembered within the fandom after its peak. I mean stuff that seemed like it was super popular for a brief while and then just became totally forgotten.
These were the sort of series that makes you go "You just had to have been there" or "It worked if you were at the right place and the right time"
You had a lot of those in the late 2000's when the anime boom was starting to go bust, but they existed before then and afterwards as well.
Some of the ones I can think of would be Elfen Lied, Fruits Basket, Vampire Knight, FLCL, Air Gear, OHSHC, Trigun, and Outlaw Star.
Cowboy Bebop might've fallen into that category had it not been the debut anime of Adult Swim and actually had a little bit of crossover appeal into the mainstream back in the early 2000's.
It's not just an anime thing, you see the same kind of phenomenon with western animation and live-action movies and shows too.