You have followed the franchise (be it a comic book title, a movie series, a TV show, an anime or a video game) with eager enthusiasm.
You got to know and love all the characters, all the stories, all the plotlines...
...and then the ending comes.
An ending that renders the entire franchise a moot point. Not just one movie, not just one issue, not just one episode, but every single installment of the franchise up to the point.
It leaves you with the rather unpleasant feeling that all the time spent watching/reading/playing was a waste of time.
When applies to a single sequel of a single work, it's Happy Ending Override. This trope is "Entire Franchise Override" (Happy Beginning, Middle and Ending Override).
Since this is an Ending Trope, beware of spoilers.
Anime and Manga
- End of Evangelion has Third Impact finally happening and all of humanity (bar Shinji and Asuka) being wiped out, rendering the entire point of Neon Genesis Evangelion a moot point (since the premise was to try and stop Third Impact from happening). Worse, even though Rebuild of Evangelion was advertised as an attempt to get the franchise back on track, Third Impact STILL ends up happening there.
- Titans/Young Justice: Graduation Day does this for Young Justice, with Wonder Girl II declaring the entire team to be "stupid, inept children" and disbanding the team right then and there, leaving the others to join a new version of the Teen Titans.
- In Terminator: Dark Fate, the young John Connor is murdered by a T-800 sent back in time by Skynet... which causes Skynet to be erased from existence and replaced with an entirely different villainous AI, Legion, and the role of "future leader of the Resistance" is shifted to Dani Ramos, someone with zero connections with Sarah Connor or John Connor or Kyle Reese - meaning the premise of the entire franchise is flushed down the toilet.
- Highlander: The Source reveals that the Prize had to be won by an act of pure love, meaning the entire premise of the franchise (immortals fighting each other to the death to claim the Prize) has been a moot point.
- In Glass, it's eventually revealed that Ellie Staple is part of a nebulous, quasi-supernatural organization dedicating to suppressing (and/or exterminating) superhuman beings. She and her organization proceed to murder David Dunn and Kevin Wendell Crumb, and Elijah Price is killed by Crumb (or rather, The Beast). This negates the entire point of the trilogy (an emerging superhero facing off against emerging supervillains). Made even worse because Elijah's supervillain codename is the title of the movie.
- ALF ends with Alf being captured by the government, rendering the entire premise of the show (Alf hiding from the government by living with the Tanners) a moot point.
- In Game of Thrones, Daenerys Targaryen goes insane and crosses the Moral Event Horizon in the second-to-last episode of the final season of the show, meaning the "Song of Ice and Fire" that the entire show AND the books had been building up to was completely pointless. Not only that, since Daenerys ascended to the Iron Throne by force, all the political intrigue and backstabbing (ie. the "Game of Thrones" that the show is named after) is rendered a moot point - and then one of Daenerys' dragons melts down the Iron Throne, making the entire show a moot point (on its very final episode, no less), because now there's no Iron Throne to claim at all.
- At the end of Camp Lazlo, it's revealed that Scoutmaster Lumpus is an escaped mental asylum patient who kidnapped the real scoutmaster and took over his job at Camp Kidney, rendering the entire show moot. It should be noted that Lazlo is as stunned as the audience by this revelation.