The ending of X-Men: Apocalypse resets the board for a new team: Apocalypse is dead, Xavier and Moira are reconciled, and the school has a fresh generation of students to train.
After Jean destroys Apocalypse, Xavier restores Moira's memories of him, and the two reconcile. Erik helps rebuild the school but turns down an offer to stay as a teacher, and Peter keeps his link to Erik to himself for the moment. Hank and Raven train a new team made up of Scott, Jean, Ororo, Kurt and Peter, which sets up the future X-Men.
In my opinion, this is the most important beat in the film. The line up that gathers at the end features the younger versions of Scott, Jean and Ororo, who appear older in X-Men (2000). Erik walking away fits his character, and it is a reminder that he is never fully part of the school. His grief in Poland also echoes the opening of X-Men (2000), where a young Erik bends a metal gate at Auschwitz after being torn from his parents. Both films tie his powers to a family loss, and, as such, his turn to Apocalypse feels like a repeat of old pain rather than a new idea.
Why does Jean finish the fight? In my opinion, it is the film's clearest piece of planning. Magneto and Storm turn on their master, and Xavier holds Apocalypse on the mental plane, but it is Jean letting her full Phoenix power loose that destroys him. That sets up dark phoenix, where Simon Kinberg, a credited writer and producer here, directs a whole film about her.
The Weapon X sequence deserves a comparison too. Stryker, played here by Josh Helman as he was in x men days of future past, holds the caged mutant, and Hugh Jackman's uncredited appearance gives a nod to x men origins wolverine. It could be argued that the brief cameo does more for the series than the Cairo finale, since it connects the younger cast to the Wolverine story without a lengthy detour.
Is Apocalypse actually the first mutant? The film presents him as exactly that. What is his actual power? On screen he can move his mind into a new body, make other mutants stronger and use Cerebro to reach minds worldwide.
Why was it hated by some viewers? It could be argued that the film asks a lot of its ensemble, with 15 billed cast members and a villain who spends much of the story recruiting. Production context may help: the team built nearly 60 sets in Montreal, including a Cairo pyramid made from an old factory, according to Screen Global Production and The Irish News, so the spectacle was not cheap. That being said, the Quicksilver sequence, which ran about two minutes and took more than six weeks to shoot, and the Phoenix finale are the parts I would point a newcomer to.