If 1993's groundbreaking Steven Spielberg classic "Jurassic Park"—and, for that matter, 2015's gangbusters "Jurassic World"—beautifully balanced eye-opening wonder and heart with edgy, thrill-ride frights, 1997's "The Lost World: Jurassic Park"—and "Jurassic World: Fallen Kingdom"—are darker, grittier, and a little less fun, sequels more concerned with the chase than the human beings being hunted. Both in terms of its tone and narrative beats, the similarities do not stop there, so one's opinion of this fifth installment will likely come close to mirroring their thoughts on "The Lost World." J.A. Bayona (2007's "The Orphanage" and 2016's "A Monster Calls") is a savvy filmmaker with a penchant for crafting nervy tension and gothic atmosphere, and here he demonstrates his key mastery on both fronts; indeed, his direction and cinematographer Oscar Faura's (2012's "The Impossible") marvelously chilling use of light and shadows are superior to the uneven screenplay (credited to Derek Connolly and Colin Trevorrow) from which they are working.

It has been three years since a cataclysmic enclosure breach led to the destruction and hasty abandonment of prehistoric theme park Jurassic World, and now the cloned dinosaurs left behind on the island of Isla Nublar are in danger of being wiped out by an imminent volcanic eruption. With a moral and ethical debate waging over whether or not to save the lives of these genetically engineered creatures, former park-operations manager/current dino-rights activist Claire Dearing (Bryce Dallas Howard) is called upon by ailing entrepreneur Benjamin Lockwood (James Cromwell) and close aide Eli Mills (Rafe Spall) to assist in transporting the imperiled dinos to a nearby sanctuary island. Accompanying Claire on this mission are her ex-beau, dinosaur trainer Owen Grady (Chris Pratt), headstrong paleoveterinarian Dr. Zia Rodriguez (Daniella Pineda), and systems analyst Franklin Webb (Justice Smith). Once back on their old stomping ground of Isla Nublar, Claire and Owen are discouraged to discover a shady ulterior motive behind what they thought was to be a noble act of animal preservation.

The opening hour of "Jurassic World: Fallen Kingdom" is textbook "Jurassic Park," electrifying in its richly designed, suspense-laden action set-pieces. The pre-title sequence, depicting an underwater expedition to extract DNA from the bones of the genetically modified Indominus rex, is a riveting rainswept opener, in one awesome shot the lightning serving to illuminate a Tyrannosaurus rex on the prowl. Following a winning reunion between Claire and Owen and an economical introduction to the supporting players, the picture is off and, quite literally, running. With the volcano erupting, the lava beginning to flow, and the humans and dinos in a mad dash for survival, Bayona cooks up one socko, armrest-clenching situation after the next. The final moments of this first act—and make no mistake, the film is quite jarringly split down the middle into two halves—might be as dramatically wrenching as anything the franchise has devised.

By and large, where the story goes from this point has been smartly and strategically hidden from promotional materials. Without giving away any major spoilers, the spatial scope narrows rather than expands, resituating itself within the foreboding corridors of the Lockwood estate. It's an admirable about-face, a twisting of expectations that effectively reminds of a supernatural horror film involving very real dinosaurs in place of ghosts. Before the high-throttle climactic payoff arrives, however, the momentum of the first hour gradually but surely slows to a crawl, bogged down in a cynical, mean-spirited plot that proves to be precisely the point but still isn't exactly pleasant to watch. There are easy ways in which this segment might have been tightened for the better. Instead, it meanders and sags for a solid half-hour that too often loses sight of the characters about whom the viewer actually cares.

The transformation experienced by Claire in "Jurassic World" was one of its most defining characteristics, and not just because she proved to be fully capable of outrunning a T-rex in high heels. An independent career woman who had nonetheless traded in her values for the bottom line, she ultimately reclaimed her soul by choosing to do what was right. Three years on from the deadly disaster which befell Jurassic World, Claire is still a dedicated professional but now doing virtuous work, having founded the Dinosaur Protection Group. That she is willing to risk her life to save the imperiled dinosaurs says a lot about the person she has become, and Bryce Dallas Howard (2016's "Pete's Dragon") is once again fierce, convincing, and sympathetic in the role. She and Chris Pratt (2018's "Avengers: Infinity War"), a steady, reliable force as Owen, have a disarming chemistry which disappointingly doesn't get much time to take shape once they are asked to take a backseat to the overstuffed goings-on around them.

In supporting turns, Justice Smith (2015's "Paper Towns") exhibits excitable charisma as Franklin; Daniella Pineda is appealing as the no-nonsense Zia; Rafe Spall (2016's "The BFG") chews the scenery while attempting—and failing—to find more than two dimensions as the greed-fueled Eli Mills; James Cromwell (2010's "Secretariat") brings quiet nobility and suggested but unspoken shades of regret to Benjamin Lockwood, former partner of Richard Attenborough's now-deceased John Hammond; newcomer Isabella Sermon acquits herself admirably as Benjamin's young granddaughter Maisie; and Ted Levine (2010's "Shutter Island") shows up in one of his signature bad-guy parts as slimy mercenary Ken Wheatley. Jeff Goldblum (2017's "Thor: Ragnarok") also briefly returns to the series as Dr. Ian Malcolm, exulting words of wisdom about the dangers of continuing to mess with nature.

There is surely enough that works in "Jurassic World: Fallen Kingdom" to recommend it, but it too frequently lacks the human warmth and prehistoric reverence which should be tried-and-true beacons of this series. Left in its place is a grimmer, more sobering aftertaste, one which enticingly sets up the next entry but left this viewer feeling a might bit chilly. What is worth dwelling upon, then, are its successes. Director J.A. Bayona knows how to expertly build apprehension in his audience while providing a haunting visual design. Callbacks to past events within "Jurassic Park" canon—the toppled-over remains of a safari Jeep here, a cat-and-mouse game not unlike the first film's kitchen-set velociraptor attack there—are affectionately woven into the story's fabric. Special effects are uniformly outstanding, impossible to tell where the CGI ends and the animatronics begin. Michael Giacchino's (2018's "Incredibles 2") music score is once more a cohesive thing of beauty, and it doesn't hurt to have intermittent assist from John Williams' beloved original themes. "Jurassic World: Fallen Kingdom" delivers plenty of individual thrills and excitement, but the film's bombastic proceedings are a touch too bleak and severe to fully achieve its aspirations as popcorn entertainment.