I liked it, but I won't pretend I wasn't also disappointed.
I hadn't believed early impressions, but Lawrence really phoned it in, and since she keeps giving inspirational speeches this murders any emotional impact the film could have. She's way too young to be Harrison Fording her way through a big movie like this.
Also had pretty major problems with Magneto's arc, but honestly all of the X-men films have this same problem to some degree. He's a villain, and even though you have likable, charismatic actors playing him he's still evil. At least Fassbender did a good job with what he had, and you can give the movie a little slack and assume that final meeting was more Xavier not being up to a fight rather than "You're a great guy, Magneto!" Reusing dialogue from the first X-men film supports this, the idea that they were bringing it full circle, though I still wanted some acknowledgment of his sins here. I'm even willing to give him a lot of slack for the police deaths, but you can't tell me those bridges and buildings we see getting destroyed were empty...
Certain fans will probably vehemently disagree with me, but ultimately the biggest problem with this movie is it felt like Singer doing a deliberately authentic X-men film for the first time. You have something like 18 major characters, many of them with insane powers, and you can't have that in a ~2 hour film and also give them the sort of things everybody expects from a decent film, like character development. In superhero comic books this sort of cast size (arguably) works, because you both have way more space/time to work in and ultimately the goal is more just to put a bunch of these unchanging action figures into crazy new situations every month. It's more comfort food for kids rather than actual dramatic art, or a soap opera if you prefer (and either way that's okay!). Comic fans don't expect things like character development -- they certainly don't get it, with rare exceptions -- but the standards are simply higher in film. In this tons of shit happens, but everybody is basically the same at the end. Singer and company are clearly trying to make a good movie, and some of it really works, but on the whole it almost feels like a MCU film and that's deeply unfortunate.
(I like a lot of comics, even super hero stuff, but let's not pretend 95% of them aren't disposable nonsense for kids with no higher aspirations.)
The Weapon X stuff bothered me a little, but it was also largely inevitable even in context of Days of Future Past. (The future was shown to change in ultimately very small ways, though obviously they hinted at bigger changes out of the frame.) They still should have thrown some kind of line in there about how Stryker got Logan in the end or similar. It's easy to make perfectly reasonable excuses for it, but for something that was the exclamation point at the end of the previous film we shouldn't have to.