Endings in comics are hard. Not only do writers have to deal with ongoing continuity, so endings aren't technically 'endings', they also have to wrap up stories that have been going on for years, even decades in some cases.
Add on to this, coming up with satisfying conclusions to the quite frankly insane amount of side-characters' plot lines and arcs and comic writers have themselves quite the challenge. It's like finishing Game of Thrones, but you also have to explain why Ayra is a clone now, why the Hound's long-lost daughter (who's also evil) has finally shown up and why Bran has a snazzy new costume and electricity powers, as well as finishing the actual story.
However, when endings do happen, the combination of years of character development, epic storylines and continuity can culminate in endings impactful enough to give you chills, whether the good kind of chills where you see your favourite characters get a happy ending, or the bad kind that you remember at 3am and stop you from getting back to sleep.
These are some of the Marvel Comics endings that made readers feel tingles down their spines.