The plot is a complex one to say the least combining the endings of X-Men: Last Stand with X-Men: First Class. Essentially because of the killing of Trask by Mystique humanity and mutants are nearly wiped out. Using a mutant's power, Wolverine returns to the past and convince the young Professor X and Magneto that they must work together to change these events and stop the rise of the Sentinels. It is a clever way to bring together both original cast members with the new ones. It all boils down through twists and turns that we are who we must be and just one person can make a difference. As always, the X-Men uses the theme of intolerance at its core to make its point.
It is this character driven theme, and the skills of all the actors that makes the movie work. It is action packed with great visual effects, for certain, but it is because we care for the characters and understand their motives that we become involved. I don't think you will be displeased with X-Men: Days of Future Past. Ignore the purists and fan boys who cannot let go of even the minutest detail of the canon and enjoy. It is is well worth the extra cost of 3-D, as well. I will buy the Blu-ray.