“X-Men: Days of Future Past” attempts to merge the X-Men trilogy and “X-Men: First Class.” “The Last Stand” and “First Class,” were disappointing, but the newest installment in the franchise pulls the merger off startlingly well.

In “Days of Future Past,” the cast from the original trilogy is thrust into a dark future where mutant-slaying robots seem to control the planet. This world has a lot in common with the post-judgment day setting in the Terminator franchise, but is far more depressingly atmospheric.

With mutant-kind on the verge of extinction, the surviving X-Men hatch a plan to send Wolverine (Hugh Jackman) back in time to stop a 1973 assassination. The plan leads to a post-apocalyptic nightmare.

The 1970s sequences feature interesting character explorations. Young Xavier (James McAvoy) and Magneto (Michael Fassbender) are polar opposites in their attitudes toward humanity, leaving Mystique (Jennifer Lawrence) torn between both doctrines. This shouldn’t be new to anyone who’s seen a single X-Men movie before, but it adds a lot of compelling drama to the super-powered mayhem.

Unfortunately, Quicksilver (Evan Peters) is just as super-humanly irritating as he is fast. Also annoying is screenwriter Simon Kinberg’s insistence that mutants were somehow unknown to the public until more than 10 years after the events of “First Class.”

The movie’s greatest sin, however, is one of omission. The post-doomsday setting is the most fascinating part of the film, but is sadly underdeveloped. It doesn’t get nearly as much screen time as the parts that take place in the ’70s.

The future scenes offer better action, more interesting set pieces and more powerful drama, but they sadly take second stage to scenes in the past. This setting imbalance robs the scenes of much-needed growth. A more in-depth struggle for survival against the robotic Sentinels, as opposed to the two battles we get, would have made for a far more novel experience. Sadly, the story ends up as nothing more than a missed opportunity.

Fortunately, the ’70s-era story taking up most of “Days of Future Past” is a competent one. While it isn’t the more interesting of the two plot threads, the past portion of the plot still manages to gracefully carry the movie’s weight.