1- It's true that everybody is saying that this movie has had the worst opening of the franchise, but what can I say, they got me with the action sequences.
It has plot holes, as all the previous ones since the reboot, but I think that there are two reasons behind the underperformance: the people don't want new actors in the shoes of their favorite characters, played previously by other actors, and because there is no reason to watch a movie knowing is not going anywhere. This is the last one, and when the next one pops, it will be as if nothing of it had ever happened. It's like knowing the ending, it's not exciting anymore.
It’s said that one of the reasons for using the Phoenix again is supposedly to amend for 'The Last Stand', and it's true, but at the expense of the rest of the movie. In the previous one, Jane Gary's motivations weren't clear, she just killed without an apparent reason, and then there it was the plot around 'the cure’. However, this one it’s totally the opposite, the whole movie is about Jean's development, with some cameos from the X-Men. May be an X-MEN movie, but they are wasted.
There are two things I don't like about it: Mystique's death. It felt out of place, and a dumb way to die. It's said that the reshoots were to avoid similarities with another Marvel movie, but no one thought about redoing this scene feels the same as Black Widow's in ‘Endgame’? Though, in this case, the reason behind it is behind the cameras, as Jennifer Lawrence wanted to exist the franchise once and for all, avoiding to appear in any possible sequels. And the other reason is the end itself. Even if I like where everyone ends, they seem too happy forgetting the consequences of Jane's actions, being the mutants in danger again.