You know the drill: Some hip, hugely successful, or universally acclaimed thing comes out, gets tons of attention, is widely referenced and satirized in popular culture, and then vanishes into obscurity, receding rapidly into the collective rearview mirror, its influence quickly forgotten or denied (even if it remains, to some extent, in effect).
My pick is The Ultimates, Mark Millar's attempt to revamp the Avengers for the Gen-X/Millennial set. At the time it seemed pretty neat, ditching decades of moribund continuity in favor of a contemporary reboot set entirely in the modern world with "realistic" problems circa 2002. And indeed, the Ultimate line may have helped to popularize the concepts of both the reboot and the "grounded" re-imagining. But within a couple of years, it was already starting to look like just another superhero comic; 9/11 made Millar's efforts at depicting "realistic" comic book carnage look trivial by comparison, and almost everybody on the team came off as an asshole. In a short time, the series faded faster than Freddie Prinze Jr.'s movie career.
It's often cited as the "game plan" Marvel used for creating the movie versions of SHIELD and the Avengers, but about all they have in common is the Samuel Jackson version of Nick Fury. Whedon's origin story stuck much closer to the original Marvel Silver Age versions of the characters — Thor is an actual Norse God instead of a possibly delusional eco-activist, Cap isn't a jingoistic bully, and Millar's horrible Hank Pym is nowhere in evidence. (The movie has Millar's Chitauri, but that's almost certainly only because Fox owned the Skrulls.)