For once, you can praise a film for truth in advertising: the adjective in the title of “The Good Dinosaur,” the latest entry from the Pixar animation giant, is right on the money. The studio has made some exceptional movies in the past, but this isn’t one of them. It’s perfectly agreeable and, of course, technically masterful, but in narrative terms it’s pretty conventional, paling beside Pixar’s more imaginative efforts. That doesn’t mean that it isn’t still miles ahead of most of the competition, but to call a Pixar production just okay means that it’s essentially a disappointment.

The story is basically a prehistoric boy-and-his-dog tale, but with a twist: in this case the “boy” is a dinosaur, and the “dog” is a boy. (The dinosaur even calls him “Spot.”) It’s set on an alternate earth where the meteor that led to the extinction of dinos instead missed the planet by a hair, so the beasties survived and evolved into intelligent, home-making creatures. Meanwhile the human race is just starting its climb up the evolutionary ladder, and isn’t yet terribly advanced.

So of the two main characters on tap here, it’s the apatosaurus Arlo (voiced by Raymond Ochoa) who’s the more intellectually and socially developed. He lives with his parents (Jeffrey Wright and Frances McDormand) on the family’s corn farm, but is the shrimp of the litter, the constant butt of jokes from his bigger siblings Buck (Marcus Scribner) and Libby (Maleah Padilla). Poppa’s advice, as so often in such tales, is to overcome his fear—poor Arlo is even terrified of the family’s chickens—and make his mark by doing something important.

To help the little fellow, Poppa gives him the task of guarding the family’s food store against intruders, but when a feral human tyke (Jack Bright), jumping about on all fours, invades the larder, Arlo fails to deal with him, and when Poppa and Arlo take off after the urchin, disaster strikes, leaving the little dinosaur on his own in the wild. Luckily he and Spot make an uneasy truce and gradually become bosom companions—and protect one another—as they try to find their way back to the farm.

What follows is an episodic series of adventures that bring the duo into contact with a variety of helpful or dangerous critters. The most amusing, though unfortunately the briefest, is an encounter with a philosophical styracosaurus called Forrest Woodbush (voiced in deliciously deadpan style by director Peter Sohn) with a bunch of protectors arrayed on his horns. But a longer sequence in which Arlo and Spot join forces with a trio of T-Rexes to track down their herd of longhorns, which have become the target of rustler raptors, is buoyed by the contribution of growling Sam Elliott as Daddy Rex, whose campfire talk is a highlight, even if it—as well as the gruesome gastronomic practices of the chief villain, a nasty pterodactyl called Thunderclap (Steve Zahn, oozing menace)—might be a mite too unnerving for the littlest tots. They might also find strange a short interlude in which our heroes consume some rotting fruit and have a drug-induced trip, though another, in which Spot rips the head off a giant insect, will probably appeal to kids’ love of yucky stuff. (The customary potty humor, however, is relegated to a single sequence, and done in a fashion that’s quite discreet by today’s standards.) Needless to say, the journey ends happily, with Arlo finally showing not only his courage but a willingness to make sacrifices for Spot to have a real family, too.

This chain of rambunctious action is sporadically engaging, but it has to be said that neither Arlo nor Spot is among Pixar’s more memorable characters, and even Elliott’s Butch is more notable for the actor’s gravelly delivery than for the T-Rex’s personality. That roundup sequence does, however, help to define “The Good Dinosaur” as something of a cartoon western (a feeling enhanced by the score from Mychael and Jeff Danna), and the animators have responded with background art that is utterly gorgeous: an opening shot that looks like Monument Valley gives way to swirling fields of cornstalks and rivers running through huge, heavily forested gorges, and a dreamlike sequence in which Poppa uses his tail to raise a assemblage of fireflies in the nighttime sky has a hint of magic (though repeating the effect later on gilds the lily overmuch).

But a Pixar film in which what one most remembers is the landscape obviously has problems. “The Good Dinosaur” is burdened with a choppy, overly familiar story, obvious lessons, and characters that, with a few exceptions, come across as bland. Because of its technical finish it’s a pleasant enough way to spend ninety minutes, but not one of the Pixar classics we’ll still be remembering years down the road. Reports of a troubled genesis, including a change of directors, appear to have been accurate.

The picture is preceded in theatres by a short, “Sanjay’s Super Team,” a sort of love letter to artist Sanjay Patel’s father, in which a boy more interested in cartoon super heroes than Hindu meditation contrives a way to have his cake and eat it too. It’s a nice little fable for a time that celebrates diversity, and like “The Good Dinosaur” is marked by beautiful 3D animation.