POSSIBLE SPOILERS FOR THOSE WHO WANT TO GO IN SEMI-FRESH:
I was reading someone's poorly informed comment on an article about this movie a short time ago that detailed his displeasure at the creative team not sticking as strictly to the comics as he would have liked and it dawned on me that he might not be alone in thinking that way. While it's great to be able to hope for as faithful an adaptation as possible, it's not all that feasible to expect everything to translate to the screen exactly as it was in the comics. This is true for brand new screen interpretations of characters that have yet to have their own movie, but it's even more true for a film series that has distinctly and consistently shown to us for over a decade now that it is NOT the original comic book and is, in fact, it's own separate universe.
Also, I don't quite understand how someone could be that upset with this movie in particular for deviating from the source material a bit since it's already been done once before. X-Men: The Animated Series did its own version of Days of Future Past which was revered as one of the shiniest moments of the show's very impressive run, yet was extremely different from its source.
In that version it was Bishop who went back in time, via time machine, to stop the assassination of Senator Robert Kelly, which was the catalyst for a war between mutants and humans that left the world in ruins. In the original 1980 comic book version, it was Kitty Pryde traveling back into the body of her younger self to accomplish the same task. One of its major differences, ignoring how different the roster of characters was for the different versions, was the subplot from the cartoon in which it was believed that it was one of the X-Men who was responsible for the assassination, which was not an element of the story originally. Very different approaches with equally satisfying results, which brings me back to Byran Singer's new interpretation of the story.
The commenter who inspired this post seemed enraged by the elements that had been altered in the upcoming film version and wondered why they couldn't just keep things the same as they are in the comics.
Here's a few reasons why that would be a very bad idea:
1. The film will most likely have the same basic story as the comics. However, since they are essentially building an alternate cinematic universe for the X-Men, whether people like that or not, what they produce has to fit within the established continuity of the films rather than the comics in order for the narrative to make any sense. Since Kitty was the original body hopper in the comics, and given that in the movie the original X-Men cast portions are set in the "not-too-distant-future" while the First Class portions are set in the 70's, were they to adhere too strictly to the original comics then Kitty would have no body to hop into because she hadn't even been born yet.
2. Senator Kelly is obviously alive and well during the time frame that the First Class portions are set in as he doesn't meet his eventual demise until the events of the first X-Men movie, so sending ANYBODY back to prevent his assassination would cause anyone who knows their history to question the sanity of the one demanding it be done. There will obviously need to be a different event that serves as the aforementioned catalyst of the war.
3. There are many characters involved with the original story that have not yet been established within the lore of the film series, most notably, Rachel Summers, whose powers originally sent Kitty's consciousness back in time. Introducing her into this movie as such an integral character in a film that's already overflowing with mutants would risk producing a similar result as the one we got with The Last Stand; meaning a convoluted mess that flies in the face of all logic and continuity.
And, yes, I know that this film series isn't exactly known for its wonderfully preserved continuity. It's made many mistakes with both its translations of certain characters to the big screen from the comic page and its inability to adhere to even its OWN continuity; such as Emma Frost existing as a child in X-Men Origins: Wolverine and as an adult in First Class, or Xavier being old and bald in the beginning of Last Stand while also still having use of his legs, yet we can clearly see in First Class that he was much younger and had a full head of hair when he was condemned to the chair.
I don't believe this will be one of those mistakes, though. In fact, I believe this could be the very thing we have all been hoping for; a way to make sense of the mess that was made after Bryan Singer took off to film Superman Returns; or as I call it "Superman Lifts Heavy Things For Two Hours". It has the potential to be the "reset button" this franchise needs to erase the tragedy of the third film's existence. After this movie they can continue to craft stories along the new timeline that will inevitably be created, much as J. J. Abrams did with the new Star Trek films (and what I'm hoping he'll do with Star WARS).
In a way, Superman Returns was a sort of test run for this concept. With that movie Singer was hoping to resume the stories that Donner started while ignoring/discarding the horrors of III and IV. It didn't succeed; partly because of the enormous length of time between Donner and Singer, but mostly because it was based around the implausible concept that Superman would just chase blindly across the universe in search of a planet he isn't even sure is still there without saying a single word to anybody first. With Days of Future Past we finally have a plot device that would allow such a reset/continuation to occur plausibly without having to resort to a reboot. And I KNOW I'm not the only person who's getting tired of hearing the term "reboot".
Take this as you will. Accept it or don't. It's your choice. I will say, though, that if you're one of the people who is holding your breath waiting for a film version of the X-Men that is completely faithful to the comics in every way then I hope you have strong lungs.
I leave you with this for your viewing pleasure: