Let me start over.
X Men: Days of Future Past is an almost complete reboot of the laughably poor X-Men "continuity". By the end off this film, it is safe to assume that the events of X-Men, X2, X-Men: The Last Stand, X-Men Origins: Wolverine and The Wolverine simply never occurred, and that we have no knowledge of this universe from 1973 until 2023. This is known in comic books as a retcon, or Retroactive Continuity - bits of the film universe that they don't like have been written out, which funnily enough ends up being almost all of it.
The film opens in a dystopian 2023, whereby most mutants are dead, with those still living on the run from the Sentinels, an army of robotic mutant killers created by Bolivar Trask. In a last ditch attempt to save mutant kind, Wolverines mind is set back 50 years to 1973 so that he can attempt to stop Mystique from assassinating Bolivar Trask, the first in a chain of events that led to the Sentinel program being what it is in 2023.
The time travel aspect of this film is actually quite easy to follow after you accept this universes version of time travel logic, and it really is a very convenient way to reboot the universe. Fox now have the opportunity to make two different kinds of X-Men films - films set in the past dealing with Charles creating the X-Men, and films set in the future about Wolverine and his team. It's just a shame that Bryan Singers return to X-Men isn't as good as it could have been.
The films main flaw is that it feels like it was made specifically to reboot the universe, with quality coming second. Although you can tell that a lot of effort has been put in to make it as entertaining as possible, you can also see that elements of the plot have been forced in just to tie the original X-Men trilogy with First Class - which would be less frustrating if the original trilogy and it's surrounding films weren't immediately written out of the continuity.
Because of the huge cast on display here, most of the characters have very little screen time with which to show a personality, affecting the future portions of the film in particular. This is fine for established characters such as Ice Man or Storm as we have has at least two full films in which we get to know them, but leaves new characters like Blink and Warpath with no personality beyond how cool their powers look, which strips away some of the tension of the future climactic action scenes. In general, the scenes set in the past are much more interesting than those set in the future and the film knows this, spending most of it's time in 1973 with the younger and more interesting Professor X and Magneto. It here where the main plot of the film occurs, along with almost all of the character interaction and development.
The big surprise of this film is that Quicksilver, who looked to be the worst part of this film from trailers and promotional material, is actually the highlight. Considering that his only contribution to the story was originally intended to use a young Juggernaut until Marvel Studios announced their intention to use Quicksilver in Avengers: Age of Ultron, his scenes and his character are surprisingly well done, marking him as the most interesting addition to the franchise. I can already see him appearing as a central character in future X-Men films, providing both comic relief and one of the more visually impressive powers. It will be interesting to see how Marvel handle Quicksilver now that Fox have succeeded in making him interesting in their own way.
Days of Future Past ends up being a perfectly serviceable film, providing a clean reboot and an entertaining (if not underwhelming) retelling of the comic of the same name. Although it fails to live up to the comic it is based on, it has all the necessary emotional beats and character interaction to keep you involved in the story, and if Fox are smart enough to capitalise on the two different film opportunities they have available, then the future of the X-Men universe has never been stronger.