It's not that Monster Trucks is "bad", which would be comprehensible. It's that it is enormously dispiriting. The kind of dispiriting that causes a film shot in the spring and early summer of 2014 to receive four different release dates before it's finally quietly dumped into the hostile snows of January, almost two years after it was first supposed to see the light of day. According to at least one rumor, part of the film's enormously long journey through post-production was because test audiences despised the film's main CGI character, and the filmmakers scrambled to redesign it to be more appealing and child-friendly; based on the repellent slug-catfish thing that exists in the final shoot, I desperately hope that this is not true.

You can tell it wants to be a fun knock-off of E.T. The Extra-Terrestrial, still the plot template that children's sci-fi fantasy defaults to all these decades later. Look at all the movement! Look at the wacky effects! Look at how carefully we've made all the trucks different colors, so as to increase the visual pleasure! None of this works out at all, in part because it is so very desperate, in part because the film has the attention span of a fruit fly and keeps forgetting what its established story was about, and especially because it makes some supremely bad calculations about what kids are interested in. Simply put, Monster Trucks has the energy and tone of a movie for the very young, but its plot is founded on the great American ideal of automobile ownership. For the emotional appeals of the first act (which are not the emotional appeals of the subsequent acts) to work at all, you have to be at least close to the age when you can think about owning and tinkering with your own car and having fun cruising around with your friends, and there's absolutely nothing else in Monster Trucks that suggests that level of maturity.

Most mature of all: star Lucas Till, not yet 24 years old when they started filming, but that defies belief more than any of the fantastic doings of the plot. Till's character, Tripp, is explicitly 16, but Till doesn't register as a 23-year-old unpersuasively playing 16; he registers as a 30-year-old unpersuasively playing 23. Which makes it hard to buy him as a restless teen anxious to go out in the world and do stuff and be free of his barely-present mother (Amy Ryan, one of the most under-used actors in contemporary American cinema getting her most thankless role yet) and her bro-ey cop boyfriend, Rick the sheriff (Barry Pepper), and be even freer of the specter of his not-present-at-all father (Frank Whaley, when we finally, briefly see him). But anyway, that's the plot we've been handed, so let's run with it.

Tripp's life consists mainly of cobbling together pieces of trucks to make his own ungainly hybrid, indulged by Mr. Weathers (Danny Glover), the owner of the junkyard where Tripp works. He has no friends that we can tell and has all the earmarks of a social outcast, though he does, somehow, have a starry-eyed acolyte in the form of classmate Sam Geldon (Tucker Albrizzi). And he also, somehow, has attracted the eye of Meredith (Jane Levy, who does at least register as a 25-year-old unpersuasively playing 16), his lab partner or something who gets all weak in the knees for him despite the demonstrated evidence that he barely knows who she is and cares less. Most importantly, he's managed to accidentally cross paths with a hideous subterranean creature with a huge toothy smile that he decides to nickname "Creech" (the film at least acknowledges that this is not clever), which decides to set up inside the hood of Tripp's car, where its very particular physiology allows it to operate the vehicle at high speeds, while also granting it playful add-ons, like the ability to jump, and such. It has, inessence, become a monster truck. Do you get it? The truck has a monster inside of it, and monster trucks are also when you heavily modify a pickup by putting giant wheels on it. Paramount has confirmed that this project originated with an executive's 4-year-old child, by the way.

The monster was unleashed through the careless avarice of some venal business executives, in case you were curious, because Monster Trucks does absolutely anything and everything it can to pretend to be a 1980s movie. In this case, it's the oil company Terravex (which, okay, is clever), run by Reece Tenneson (Rob Lowe, underneath a hypnotising quantity of make-up), who is leading a drilling operation up there somewhere in the Western United States that is left vague as hell - the movie was shot in British Columbia, but I see no reason to besmirch the reputation of Canada by attempting to foist this movie off on them. It's at Reece's command, over the objections of the vaguely ethical Jim Dowd (Thomas Lennon), that the drills plow right through a subterranean pocket of water, and the film straight-up explains why it's impossible for life to exist there, or at least complex life that would be capable of functioning on the Earth's surface, but no matter. Up comes Creech, and there we have our movie, which of course involves stopping Terravex from ripping up the planet and draining oil (the creatures' food source), but only when screenwriter Derek Connolly, working from a story by Matthew Robinson and Jonathan Aibel & Glenn Berger (the wildly inconsistent duo partially responsible for everything from Kung Fu Panda to Alvin and the Chipmunks: Chipwrecked), can be bothered to remember that the oil company is supposed to be a part of this movie.

The whole thing is wearying, confronting us with the spectacle of a great many people trying very desperately to convince us what FUN we're having, but the seams show all over the place and Chris Wedge's directing has the whiff of flop sweat, compensating for the threadbare concept and muddy plot development with manic comic routines. I cannot in good faith call any of this excessively bad - the effects are surprisingly good, considering all of the potential strikes against them, and the pacing is bright at least. It is, however, enormously and pervasively dreary and mediocre: loud, fast, messy, and almost totally bereft of good performances, other than Lennon, who plays things unexpectedly sincerely, and Levy, who has apparently pretended that she and Till are the leads in a puckish romantic comedy rather than an idiotic kid's film. That's enough to keep it from being unendurable, but it's really not much more than that.