Not many people liked the original shot at the "Dark Phoenix" storyline ("X-Men: The Last Stand") - I mean, who the hell gives Brett Ratner anything they value? That movie has been retconned out of existence, and Fox decided it was time to try the Dark Phoenix storyline again. This time they handed the project to Simon Kinberg - who wrote, produced and directed (his first directorial gig) this whimper of an exit strategy. Looking at Rotten Tomatoes today, this hasn't played well for them: "Last Stand" is at 57%, and "Dark Phoenix" is at 23%. I knew all this going in, so why did I watch it? I'm a superhero completist, at least when it comes to movies.
Sophie Turner returns as Jean Gray. On a contrived rescue in space to save a bad space shuttle mission, Jean absorbs ... a thing, an energy source. And a bunch of evil aliens want it. Jean's new power is hard to control and apparently causes mood swings and paranoia. This alienates her friends, and then she's manipulated by the evil alien leader.
I kind of enjoyed the final fight scene: it was long, and reasonably well constructed. But overall the movie is silly and not worth your time.