The cast members who had all stuck around since First Class had to sign all-new contracts to appear in this, and Jennifer Lawrence has stated that she "... kind of fucked [herself]" by doing so. That's what you want to hear when you're desperately trying to fit your franchise into the Disney mold! Then there's how even the writer/director admits that it's a loose remake of an X-Men plot from a film that came out 13 years ago, which he'd already messed up.
And then came the delays, as the movie had its release pushed back over a year to get a bunch of reshoots done and to rework the third act. Then it got pushed back five more months because the trailer did really well in China and they want it to have a better shot there. Meanwhile, all we have to go on is this trailer, aka a montage of scenes that seem to have been collected from better X-Men films: