Some things were good: the "go back in time to change the future" conceit was surprisingly unmuddled (and, despite the conceit's ubiquity, it felt...unadorned here!); the futuristic Sentinel designs were really, really great (it's hard to imbue boring evil robots with a true sense of menace!); Fassbender is a terrific actor.
I think there were more things in the movie that I didn't like than that I did, though. The final act is pretty non-sensical (why didn't Professor X just control Trask? how come Magneto can control the Sentinels, which were explicitly mentioned as being non-metallic?); the 70's setting and ham-fisted addiction allegory felt extraneous; a lot of non-Fassbender performances were pretty phoned-in.
Still, it was a romp. Superhero movies can have a lot of extraneous garbage and this was not one of them. There was a clear through-line to the entire enterprise, and the grounding of the melodrama not in Big Bads or anything too cosmic (looking at you, Marvel!) but in interpersonal relationships & agency are what make the X-Men stories so unique and resonant.