This is about as serious a comic book superhero movie as anyone is going to make. And because of the history we have with these characters, it works. Its an interesting question to ask how well it would work if we had never encountered Wolverine or Prof X before, but regardless, that’s not the case here.
In this third wolverine movie, Logan is now old and his powers are waning. And to be honest, that is a really interesting idea after watching this character be able to hack and slash through people without any real consequence. We also see Xavier as a broken old man grabbing for any sort of happiness; also interesting. This movie also has Dr. Carter from ER. Interesting.
So anyway, what we get is a pretty hard-edged X-men film which really hints at notes of deep sorrow, defeatism, and even nihilism. But it still remains a superhero movie. So its still fun to watch, but its also not at the same time somehow.
As far as the ending, all I will say is that they could have went two different ways, and I think either one would have suited. They had to choose one way, but I can’t help but think if I would have preferred the other. Still, a very strong last effort for Jackman in these X-Men films. What a great wolverine he turned out to be.