Samuel L. Jackson’s Elijah Price, or Mr. Glass, as he prefers to be called, was by far the most compelling part of M. Night Shyamalan’s slow-burn comic book send-up “Unbreakable.” A brilliant, tortured manipulator and superhero enthusiast suffering from osteogenesis imperfecta (i.e. brittle bone disease), Glass is that kind of charismatic supervillain that you can’t get enough of.

Nineteen years is certainly a long time to wait for more Mr. Glass. But Shyamalan, even after naming this long-gestating film after Jackson’s character, decides to withhold him from the audience even longer. Yes, he makes Mr. Glass a highly sedated vegetable who gets to do little more thank blink and intensely stare at the camera for what feels like more than half of the movie.

It’s one of the many ways in which “Glass,” which seems to delight in building up anticipation only to pull the rug out from under you, manages to both frustrate and underwhelm. I’m sure it’s some kind of meta-commentary on the futility of serialized storytelling, the contrivances and deification of comic book culture and easily malleable audience expectations, but in execution it mostly feels like a tub full of half-baked ideas that never really coalesce into something exciting, meaningful or all that memorable.

“Glass” definitely doesn’t care to help if you haven’t seen “Unbreakable” or “Split,” either. It just dives right in with little exposition. We see Bruce Willis’s David Dunn taking a couple of teen pranksters to task. Then it jumps to James McAvoy’s multiple personalities, who’ve decided to take four teenage cheerleaders hostage because they’re “impure” and “need to be punished.”

David, who is working alongside his now-grown son Joseph (Spencer Treat Clark, the same actor from “Unbreakable,” which is actually a nice touch), has been trying to find the missing cheerleaders. Joseph warns him to be careful, because David has also been branded a public nuisance for all of his would-be good deeds that have left criminals and victims injured and looking for someone to sue. If you’re thinking, wait, isn’t this sort of the plot of “Incredibles,” just wait because it even brushes up against some “Incredibles 2” themes, intentionally or not.

David and the “Horde” (the term used to describe the collective of all of McAvoy’s personalities, which range from a 9-year-old boy and an older British woman, to a terrifying flesh-eating creature called “The Beast”) meet and low-budget fight a bit, but are interrupted by the authorities and Sarah Paulson’s Dr. Ellie Staple who take them to the psychiatric hospital where Price is.

Dr. Staple explains with oozing condescension that she specializes in treating those afflicted by delusions of grandeur — aka, those who think they have superpowers. She says their abilities and their weaknesses are all in the mind, and can be explained away by science and childhood traumas. This little group therapy session in a bubblegum pink room is one of the more compelling parts, and it seems like the film is gleefully destroying the superhero origin story myth, sending its main characters into a spiral of doubt.

But don’t get too attached to this, or any other path Shyamalan seems to be taking us down, because he will change course, backtrack and laugh at you for getting too committed to one narrative (while really going all in on some questionable ones, like having the Horde’s sole surviving captive from “Split,” Casey (Anya Taylor-Joy), come back as a sort of Stockholm Syndrome empathy machine to worry about him).

Mr. Glass does emerge from his vegetative state, eventually, and kicks the movie into gear as only Jackson can do. McAvoy is once again giving his all to all the characters, and watching him shift between them is still enjoyable, but perhaps not worth all the screen time it gets. Willis barely gets anything to do at all. But for all the hype behind these three characters meeting, and the years it took to get it off the ground, “Glass” is one big anti-climax.

“GLASS”

**

(PG-13, 2:09)