(CNN) The Phoenix Saga in the X-Men comics of the 1970s is rightly considered a classic of the genre, which explains why filmmakers keep returning to it. Yet the hope for a truly definitive take on the story, "Dark Phoenix," proves a tepid addition to the "X-Men" cinematic series, while possessing just enough merit to prevent entirely going down in flames.

Grading on a curve of recent X-Men movies, place "Dark Phoenix" well behind the "X-Men" editions subtitled "First Class" and "Days of Future Past" but ahead of "Apocalypse," the latter representing the nadir of the mutant heroes.

Notably, "Phoenix" shares a weakness with that most recent film -- namely, an utterly mediocre villain. In the process, it doesn't entirely squander the cast headed by James McAvoy and Michael Fassbender -- whose screen chemistry as Prof. Charles Xavier and Magneto has provided the backbone of these movies -- but nor does it maximize that talented pairing or the broader material.

For those who didn't spent the '70s reading X-Men comics, the bones of the story hinge on Jean Grey (again well played by "Game of Thrones'" Sophie Turner), an enormously powerful mutant who has grown up under the tutelage -- and indeed, control -- of Xavier, who has sought to curb her potentially dangerous abilities.

This underlying template also found its way into the sequels in the original trilogy -- culminating in "X-Men: The Last Stand" -- although again, in a manner that didn't wholly translate the qualities that made the characterization of it as a "saga" more than mere hyperbole. (The 1990s "X-Men" animated series, frankly, probably still has the best claim to having put the story on screen.)

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