Xavier is very well and believably played by James McAvoy and Lensherr by Michael Fassbender. The creditable acting ends there. Most of the other cast were difficult to watch. While January Jones' lack of emotive ability is no surprise, it was the "mailed-in" performance by Kevin Bacon as evil Nazi Sebastian Shaw that was unexpectedly wooden and bad.
One last quibble with the concept of a prequel is the lengths the story goes to explain the origin of every last aspect of the previous movies. Do we really need to know the origin of the telepathic blocking helmet later used by Magneto or the X-plane? The entire concept of the X-Men requires suspension of belief to a great degree, therefore many things do not necessarily need to be accounted for, in my opinion.
Although I had some issues with the acting and the story, it was still a fairly enjoyable and mindless popcorn flick. I thought it was better than Wolverine, but not quite as fun as the three original films. Due to language and some more adult situations, I would recommend this film for older teens and adults only. The USCCB has yet to review X-Men: First Class.