I saw it last night, my first viewing. I think overwhelmingly positive reviews will give it a solid second weekend.
I wouldn't say this is the 'best X-Men film' because, to me, it isn't really an X-Men film. But it's the best Wolverine movie.
I found the first half very slow, i was wriggling around in my seat. The action/superpower scenes are good (Xavier's seizure stopping the attack in the casino; the attack at the farm; and the final showdown in the woods). Dafne is great as X23. I didn't get at all emotional. And the use of Shane footage/dialogue felt a bit heavy-handed.
I enjoyed the acting from Patrick Stewart, Dafne Keen and Boyd Holbrook, in particular. Jackman was good but still a bit flat and emotionless for me.
Caliban wasn't really vitally important/useful to the plot, in my view.
The timeline/continuity is weird as ever, expecting me to believe all this happened just six years after the 2023 happy future epilogue of DoFP. Felt like it should have been 15-20 years later. 2039 would have worked better. But the whole feel of the movie was more of a standalone.
Also, they dwelt a lot on the X-Men comic books not being anything like real life. Seemed very much like Mangold giving the middle finger to comic book fans. But the comics are where Wolverine and Xavier come from originally, not sure why they were treated with such contempt as nothing but fairy stories.
It's very good, there are no technical issues (like bad VFX etc), the writing is very good ('this is what life feels like'.., though it's Patrick Stewart who sells the line). I would give it a 7.5 or 8 out of 10. My friend felt it was a solid 8. He enjoyed it more than me and had no quibbles at all but he admitted he also noticed the over-use of Shane and the contempt for the comics.
I'm glad they didn't use Omega Red instead of X24, he's better kept for an X-Men team movie and would have been out of place here. Someone else's suggestion of an elderly Magneto appearing at Eden and drawing the metal out of Logan so he could spend his final years with Laura might also have worked though, and perhaps would have been more unexpected than Logan's death (which seemed like the obvious thing that would happen).