Over 11 films and roughly 22 hours total running time, not a single one of the Avengers has gotten so much as a scratch. They're supposed to be good at what they do, but when they're virtually invincible, the tension is severely diminished. X-men, meanwhile, are knocked off all the time - even if they might later make a return, producers frequently find a way to despatch core characters in brutal ways. Along with the ungodly massacre that was The Last Stand, which took a Game Of Thrones-style approach to disposing of its leads, there was First Class and Days Of Future Past, which between them killed off all but a few of the titular 'first class' and used time travel logic to kill the original cast off (before bringing them back at the end). Where you could go into Age Of Ultron pretty certain about who was going to make it out alive - that they'd already been contracted to planned future films spoiled it a little bit - you can't really be sure what's going to happen in X-Men: Apocalypse. Now the timeline's been altered, literally nobody's safe.