This movie basically invalidates the events of all previous X-men movies except X-men First Class. Warning, spoilers abound.
In the future, most of humanity + mutantkind has been wiped out by Sentinels, which are Robots designed to kill mutants/anyonewhospotentiallyamutant/anyonewhocangivebirthtoamutantinthefuture/anyonewhosedescendantscangivebirthtoamutant....Yeah, that list gets a bit long, hence why most of humanity has also been wiped out. Apparently in the X-verse, they never had films like the Matrix showing them why mass numbers of Robots are bad. So there's a last ditch plan to send Wolverine's consciousness back into the past to try and avert the events which led to this current debacle; which is Mystique killing Tyrion Lannister. Cause if that happens, Winter comes.
So anyway, Wolverine is sent back into the X-men first class period, except 10 years later on. There he meets emo Charles Xavier, concocts a plan to break Magneto out of jail to get his help, stop Mystique from killing Trask and save the world. Except basically Magneto reneges and goes onto his own agenda, which turns out to be strike down the human race first before they can fully develop the Sentinels of the future. I mean who could have seen that coming -_- Magneto's normally such a well-adjusted guy too /sarcasm. Meanwhile Mystique is also hell-bent on revenge against Trask as he's responsible for the deaths of Angel/Azazel/Riptide/EmmaFrost/Banshee from Xmen First Class. Basically everyone they couldn't be bothered to bring back for this movie. Meanwhile, we have juxtapositions between 1973 Xmen and the Bad End Xmen, who are hiding/defending Wolverine's body from the Sentinels so he can complete his mission in the past.
In the end, things happen predictably enough. The Xmen of the Future get into a desperate last stand situation with the Sentinels, being wiped out almost to a man while the Xmen of 1973 get into a desperate last stand with Magneto to prevent him from killing President Nixon. Things resolve to their inevitable conclusion and the Xmen save the day, thereby averting the bad end and rewriting the events of X1-3. How reconned is it? Basically Jean Grey and Scott Summers are STILL alive when Wolverine time travels back to 2023. Not only that but Mystique is no longer the evil bitch she was in X1-3 either. Basically, lots of ripples, shit changes.
Some of the things in the movie did have the comic book fan in me screaming. Like how Kitty can now send people back in time with her mutant powers. WTF dude? When did this happen? Also, the fights between Xmen and Sentinels, it seems like Blink would be the most powerful of the lot against the Sentinels considering she can sever their bodies with dimensional portals. There's pretty much no stopping a dimensional portal. Old Magneto somehow gets hit by flying metal shrapnel and mortally wounded, taking him out of the fight in the future. I mean...the master of magnetism couldn't block ...metal. But he can block bullets. Wtf? The reason for sending Wolverine back instead of Charles. Cause his mind can heal faster than anyone elses. Uh...then why did he have amnesia for the better part of a few decades? The level of technology in 1973 is way too anachronistic. We've got apple-like design back in the 1970s, working taser guns (first finished in 1974 and not 1973), super giant robots etc.
And then we've got the unresolved mysteries. Like what actually happens now between 1973 and the present? What really happens during the time of X1-3 now that Scott and Jean are alive somehow. At the end of the movie, when we see past Wolverine being dredged out of the river by a grinning William Stryker, we find out it's Mystique and not Stryker. What happens? Does wolverine still go through weapon X since it's not Stryker rescuing him but Mystique? We never actually do get to see if future Wolverine has his adamantium claws but Wolverine without adamantium claws is like Spider-man without web-swinging.
Overall, I'd say this is a decent movie. It's formulaic as heck, and the plot can be seen from a MILE away with no really shocking developments. Except Scott and Jean's sudden revival for no damn reason. Overall, in terms of the Marvel films released this year I'd put it below Captain America 2: HAIL HYDRA edition and above Amazing Spider-Man 2. Also, they really needed more Quicksilver in this movie, he pretty much could have solved everything by himself.