Samuel L. Jackson in 'Glass' (CNN)"Split" was a surprise hit for director M. Night Shyamalan, but its most satisfying gambit came in unexpectedly setting up a sequel to his 2000 thriller "Unbreakable." The result, "Glass," isn't a breakthrough, but proves just clever enough to come out on the right side of a split decision. Following "The Sixth Sense," "Unbreakable" seemed to herald Shyamalan's arrival as a major filmmaking talent. But then his career took a wrong turn, with conspicuous misfires "The Village" and "Lady in the Water," and has careened along somewhat unevenly ever since."Glass" marks an understandable impulse to rekindle that early flame, while struggling at times in stitching the older movie and more recent one together. After a promising start, the writer-director labors toward the end in conjuring his trademark twists, before offering what feels like a reasonable resolution to this whole experiment. Ultimately, "Glass" maintains a solid sense of tension, while like "Unbreakable" wrestling with the mythology that surrounds comic books and superheroes -- a theme that seems more timely now, with such fare dominating the box office, then it did when the century began. The premise again creates toothy roles for the film's stars -- James McAvoy, with his multiple personalities, including the superhuman Beast; Samuel L. Jackson, as the evil genius Mr. Glass; and Bruce Willis, as intrepid, reluctant hero David Dunn -- along with a more thankless one for Sarah Paulson as the psychiatrist convinced she can cure them of the shared delusion that they possess extraordinary powers. Read MoreAn introductory sequence brings the trio together in the psychiatric hospital that Paulson's character oversees, although, despite the creative efforts to confine them, it's pretty clear that can't last forever. As a consequence, even the quieter scenes are imbued with a gnawing sense of dread. Samuel L. Jackson, James McAvoy, Bruce Willis in 'Glass' Where "Glass" starts breaking down, unfortunately, is when the action kicks into motion, which proves to be something of a letdown and overly convoluted. Part of that has to do with the necessity to service both films, when "Unbreakable," frankly, is the far more interesting foundation. Although it's easy to admire McAvoy's dexterity juggling personalities, the "Split" character simply isn't as compelling as the understated duality that the first movie established. Shyamalan does provide deft smaller touches, among them bringing back one-time child actor Spencer Treat Clark as Dunn's son, all grown up, whose loyalty to and belief in his dad provides an emotional core to an otherwise rather chilly story. Taking all those factors into account, the overall level of appreciation for the movie will likely boil down to one's expectations going into it. Those who come in hoping for more should consider "Split's" limitations. For those intrigued but not anticipating too much, it's the sort of flawed but reasonably entertaining.