Regan Inglis’s review published on Letterboxd :
This is the way the X-Men film series ends: not with a bang, but with a whimper.
After various reshoots and rewrites and consistent delays, 'Dark Phoenix' ends the franchise that has lasted nearly 20 years with a dull and uninspired final entry.
I'm terms of positives, all the actors involved (save for Jennifer Lawrence, but that's expected at this point) are great, in particular Turner and McAvoy. Their performances are far better than this film deserved, even if everyone feels really low energy. The visual effects are mostly consistent and the score by Hans Zimmer is... interesting, though the lack of the John Ottman theme from the previous films is sorely missed.
I didn't feel hatred towards 'Dark Phoenix', it's just a woefully misguided attempt to retell the comic book storyline that comic book fans love. I still think it should have been done over several films, especially considering it's called 'The Dark Phoenix SAGA' - you can't expect to do it justice in one film (that's less than two hours long) when it's such a big story.
In the end, the film was pretty much exactly as I feared: a boring mess of a story that fails to live up to the expectations of the comic book. Here's hoping Marvel Studios can do it better.