^ the X-Men Animated Series did a fantastic job with this movie's same story line: Days of the Future Past, which will obviously be both a sequel and a prequel
plot lines with time travel can get a bit too verbose, but if they keep it streamlined and just have fun with the source material and play up to its unique style - this should be a wonderful film
I really recommend X-Men First Class. it was like X-Men meets James Bond, set in the 1960sish as well