Akira was, obviously, the launch off point for Anime in the west, and the movie was great. But later on I read the Manga, and they were so much richer than the movie. It seems like a 12-episode Anime would be perfect for Akira. And it would probably be successful, because everybody knows/loves it.
20th Century Boys is a bit... odder. I've read the Manga twice, and I know that there's a live action film, but the work seems so much better suited to Anime. I don't know how it's held up -- certainly no one on KIA2 mentions it. It's also not great -- the build up is fantastic, but the denouement is... odd.
Just wondering if there's a reason for this, or if it's just an historical quirk.
Akira wasn't the launch point of anime in the US, and honestly, the film was lackluster to me. Great animation, crappy story. I didn't like a single character in the film.
There are a lot of reasons why Akira didn't get a series; the film didn't really do well in Japan outside of otaku circles, and given its budget, that didn't help.
Not sure why 20th Century Boys didn't get an anime other than it looks to me less appealing to younger audiences given what the anime looked like at the time it was released in theaters. Plus with 2 live action films made it would seem like a step back to make an anime series.