Owen Hughes’s review published on Letterboxd :
It follows on from where the previous film finished off; "Senator Kelly" and William Stryker, an anti-mutant head military type guy, are at the White House talking to the president about 'what's to be done with these mutants' following (quite possibly the best opening scenes of any superhero film) Nightcrawler's attack. Magneto is boxed up in a plastic room with no means of escape. Wolverine is struggling to understand his origins. Rogue has boyfriend issues with Ice Man. Jean and Cyclops (who is massively underutilised throughout both films) are having a bit of a rocky relationship since Logan appeared. Eventually they all have to work together to stop Stryker from using Cerebro and a mind-controlled Prof X from killing all mutants.
It's good. I would probably even stretch that further and stay it's very good. After everyone is established (or at least introduced) in the first film, a lot more time is spent on building up each of the important characters to make them more interesting this time. Jean, in particular, is given more room to flex and expand, whilst more of the younger students are introduced/improved upon. Rogue is also substantially less annoying.
The story is stronger too, Stryker providing a much more convincing evil villain than Magneto was. I think mostly because you still kind of rooted for Magneto a little bit as he was easier to empathise with due to his background and what he represented (the oppressed homosexuals, blacks, jews etc) but was still a little OTT in his methods perhaps.....! Stryker is just plain evil, emphasised even more so when you see his son.
I think it's a very entertaining film without being full of explosions or fight scenes. It has a nice balance of action and story telling with subtle meanings/hints to much more real concepts than mutant superheroes. It's a shame the third film didn't get this right and that Singer didn't get to complete his story the way he wanted to. Still though, this is definitely one of the best superhero films made.