"Apocalypse Fatigue" is a term I coined to describe a phenomena in mainstream comics, where companies have ever escalating levels of destruction and cosmic catastrophe in their titles, in order to titillate readers who are immune to the normal progression of comic book plots.
For those who are not familiar with comic book history, (and for some of you who are), the reason that Apocalypse Fatigue set in has to do with changes in comic book readership. Back in the day, comic books were a form of mass entertainment mostly directed towards children and young teens, and were considered fairly disposable. A plot would have a straight forward battle between the heroes and some villains, usually over a plan to rob a bank or jewelery store. The hero would defeat the villain, usually using a clever gimmick, and all of the events of the story would be forgotten by the next issue. The comic itself was usually discarded, which is why Golden Age and Silver Age comics are worth so much now. As the 1960s started, some comics, mostly Marvel titles, brought in longer plots, and continuity. Characters from the different titles interacted with each other, which both gave a sense of a more cohesive universe, and also helped cross-market comic book titles to fans. Comic books started appealing to older readers, but they still needed to appeal to newer readers and younger readers, so while the stories could be longer and more complicated than a simple "stop the bank robbers", they still needed to be somewhat simple.
In the 1980s, after two decades of comic books being more complex, the comic book companies started marketing to older readers and collectors more. Companies started realizing that "big events" might generate interest and speculation. Also, creators took themselves a bit more seriously, (and some would say too seriously), and so were able to try more ambitious storylines. With DC's Crisis on Infinite Earths and Marvel's Secret Wars, the modern crossover event was born. It seemed to do well enough that companies would make crossover events a popular event by the late 1980s. And of course, for a big crossover event, you need a big story. And that story was always a catastrophe, often a world or even reality threatening one. The Marvel universe was threatened by near omnipotent beings in Secret Wars II, The Infinity Gauntlet and The Infinity War, which made the invasion of Manhattan by demons in Inferno and by the Atlantean army in Atlantis Attacks almost pedestrian.
And that is what the problem is with these events, that further and further levels of cosmic destruction were needed to keep jaded fans interested. But once that had been done, any story where a flagship character wasn't killed would seem trivial to fans, let alone gaining outside media attention. This also made the stories internally seem a little weak and inconsistent. In a world where the Fantastic Four have a portal to the negative zone that spews out invaders every few months, non-super characters still act as if they live in our world, not a world where intergalactic and transdimensional are common. Externally, comic book readers got tired of the whole thing.
There are two different things that have made apocalypse less fatigue inducing. The first is the fact that a good writer can make it interesting, especially if they make it smarter, not bigger. During Grant Morrison's (and to some extent Mark Waid's) work on the JLA, each story arc had the world being threatened, but it was resolved in an intelligent way. One of Morrison's trademarks was to have the world threatening circumstances ended by a small, clever plan, rather than a cataclymastic firefight---such as the scene of Batman fighting off White Martians using a match.
Another thing both companies have done lately is do stories where the apocalypse is done through characterization and storytelling, rather than through sheer firepower. Marvel had the Civil War storyline, which dealt with issues of civil liberties and ended up with super heroes fighting each other over ideology. DC had the Identity Crisis storyline, which had some very visceral elements---after the wife of a superhero is raped by a supervillain, some of the heroes magically lobotomize the villain, and then cover it up. I have to say that after being jaded by storylines where the entire world was threatened, I was surprised that I could still be affected by a story. Single panels of the Identity Crisis storyline are more visceral and surprising than the entire Our Worlds at War saga. However, even with this I am worried about where it might go next---after dealing with this issue, will readers become immune to such stories, and need something even more to shock them into interest?
Big storylines are a part of modern comics, and can sometimes be done well. Although writers and editors can mess it up through megalomania, the alternative would seem to be to having characters go back to fighting bank robbers in ten page stories.