Some light spoilers here, not like there's much to spoil...
I had not liked the previous movies much because they were way too emo and way too focused on Professor-X, whom I have a hard time giving two cents about. Magneto has had a draw for me since they established his canon as a Holocaust survivor but watching him face off with Xavier in the past movies hasn't excited me. His past plays big in this movie as does his internal struggle to find his true nature, but it's a part of an evolution, not a central tenet. Michael Fassbender continues to turn in excellent performances as a man tortured by events and loss he can't control while he struggles to control himself. James McAvoy is more tolerable in this movie than in any other so far. I appreciate the scriptwriters getting away from his internal struggles and letting the movie be about the events sweeping over the characters.
As mentioned, Jennifer Lawrence pretty much steals the movie as Raven/Mystique. She's tight, focused, but never out of control. She's learned and evolved from when we last saw her and the ending scene of the movie just melted me. I know we're supposed to be getting another Wolverine movie - and Hugh Jackman shows up briefly here to set the scene for that - but man I want a Mystique movie.
Oh, the plot? It's not terribly interesting. There's a bad guy; he's very old and very powerful because he can transfer his consciousness into new bodies, from which he absorbs powers. Why he needs a machine to do this and where he got that machine and/or learned to operate it, never mind rebuild it completely from scratch... enh, who cares. There are some weird mental powers involved, too. He can get into Professor-X's head and then take over a bunch of minds just enough to get them to launch nuclear missiles so that the missiles can be destroyed? This clears the way so later he'll use Magneto-on-steroids to destroy the world more slowly. Why he'd do that when he has the entire world's nuclear arsenal under his control is... because reasons.
He also seems to need assistants because ego, I think. He finds mutants and soups up their powers so they can serve him better, but still not better enough to prevent the peasants from revolting. It's always the peasants, or the royal guard. I think Apocalypse-qua-Apocalypse is the weakest part of this movie. He's only interesting for the changes he forces and the decisions he requires others to make.
Lots of those decisions play out during and around the final battle, which I think does better as a superhero-on-superhero fight than the airport mess in Captain America:Civil War did. Nobody here feels superfluous, though they had to nerf Psylocke way down from her comic-book powers. She's cool but doesn't really signify much. Angel and Nightcrawler do better because they've faced off once before.
Oh, and spoiler alert for people who never read comics: if they tell you someone's dead and you don't see a body you can be sure they're NOT dead. Even if you see a body you can't be sure, but they might be. However, no body is definitely not dead, however much filial angst might be displayed.