4. Dark Phoenix
It feels really strange looking back on the era of Dark Phoenix because everybody knew it was going to be awful before its release. And then it was released and it was worse than expected.
The film was Fox's second attempt to adapt the Dark Phoenix storyline, but after it didn't go too swimmingly in X-Men: The Last Stand, expectations weren't too high here. Justifiably so, it seemed. Dark Phoenix attempted to be darker than the recent X-Men movies and that just made it joyless. Nobody wanted to see the death and destruction it objected the beloved X-Men too and critics felt that it was an incredibly disappointing end to the franchise, especially when Logan did such a poignant job ending the original X-Men saga two years prior.
The younger generation of X-Men in the "prequel movies" were really building towards something with First Class, and Days of Future Past but a misstep in Apocalypse and the complete failure that was Dark Phoenix brought the franchise crumbling down. The saga's future was already in doubt when Disney bought Fox, but it would have been nice to see the heroes go out on a high. Unfortunately, it wasn't meant to be.
It's hard to argue with the negative response to this one. What a sad, sad way to end one of the most revolutionary movie franchises of all time.