Fassbender and McAvoy are the definitive version of their characters. This continues onto the third installment where Fassbender is as great as ever. There are also solid performances from Isaac and Lawrence in addition to the very fun new cast. The film is very well directed, and has great standalone sequences throughout, which much for every X-men fan to love. One thing that this trilogy has succeeded in is the dynamics between Professor X and Magneto, the trilogy has also succeeded in having emotional heart and genuine feelings, with this one being the most effective. The film also cleverly changes so much about the characters we already know, giving fun spins that are new, creative, and unexpected, taking advantage of a new timeline. Is this movie underrated, that would be a wholehearted yes.
The film is not successful when it comes to the villain or villains. Isaac gives a solid performance, but his plan is over the top, making his motivations cliche and unclear. The four horsemen, or the other three do not have much to do besides look cool, which is disappointing. In fact, some supporting X-men could have been more fleshed out in an extended mall sequence. Though some situations felt convenient there is also a lot of fan service, which may be a good or bad thing depending on the viewer.
Overall, those who watch this have to have watched the first two installments to have a full impact on this film. Singed has made a very solid film filled with heart and wonderful protagonist characters.