26. Legion of Super-Heroes: The Greak Darkness Saga
by Paul Levitz and Keith Giffen
Published by DC Comics
This is it -- the single greatest Legion of Super-Heroes story ever. And while it is part of an ongoing series, it was and remains a strong, stand-alone graphic novel.
Darkseid (before he was so overdone in the DC books), and the slightly older LSHers, this one was a different take on the idea of young heroes. Replacing the great hopefulness of the previous books with a "Great Darkness," this is one of the more underrated books that helped usher in the dark and gritty comics movement.
Only, rather than just being gritty for the sake of being gritty, The Great Darkness Saga never loses sight of the fantastic story at its core.
For the "rules" I'm using for graphic novel, check the original post.