If Hunter S. Thompson were to write a story about his trip to a parallel, prehistoric dimension, then Land of the Lost might be the most accurate representation possible of its subsequent film adaptation. Directed by Brad Silberling and starring Will Ferrell, this update on the Sid and Marty Krofft television series from the 1970s is the strangest, filthiest summer movie I think I've ever seen – and it opens against one that features Mike Tyson, a tiger and Zach Galifianakis. But just as strangely, it's also damn entertaining, although it's hard to know whether you should or definitely shouldn't be indoctrinated beforehand to its weirdness. Regardless, Land of the Lost offers a sobering alternative to the pre-packaged and otherwise conventional blockbuster fare offered by studios this summer, even if its charms would ultimately benefit from (if not require) chemical enhancement of some kind to be properly enjoyed.

Ferrell plays Dr. Rick Marshall, a disgraced scientist who unexpectedly gets a second chance to test his radical theories on time travel after getting sucked into a space-time vortex with a research assistant named Holly Cantrell (Anna Friel) and a huckster tour guide named Will (Danny McBride). Landing in a parallel, prehistoric dimension, Rick forges a tenuous friendship with a primate named Chaka (Jorma Taccone) even as he insults or otherwise offends virtually every other living creature, including a foul-tempered Tyrannosaurus Rex. But when Rick, Holly and Will stumble across Enik (John Boylan), an outcast member of a mysterious race of creatures called Sleestaks, they inadvertently become embroiled in a plot to conquer Earth, and must try to prevent an interdimensional invasion - even if it means they can never return home again.

Most importantly, and in the interest of protecting young, corruptible minds, Land of the Lost is absolutely not for children. There's at least one f-bomb, Rick and Will talk about Sleestaks "tapping that ass," and there are multiple sequences in which our heroes are violently threatened by a Tyrannosaurus – although he is nicknamed Grumpy. Like many, I was prepared for, well, a movie based upon a kids' television show, and expected something more like Ferrell's Elf, albeit in a prehistoric setting; instead, I essentially got a Jurassic version of Anchorman, which suggests... if not maturity, necessarily, then at least humor that's decidedly for grown-ups.

Not unlike Anchorman, much of the film has an improvisational quality, which is certainly uncharacteristic for effects-laden blockbusters, but it distinguishes Land of the Lost from much if not all of its summer movie competition. Specifically, its set pieces are jumbled together, its CGI wildly inconsistent and its story structure virtually incomprehensible, at least once you realize that minutes of screen time have passed without anything in particular happening. But at the same time, you do have to actively realize that, and what the film possesses in spades is a certain kind of fearless, seat-of-the-pants ambition that doesn't always succeed but generally distracts you from the fact that it's failing.

A centerpiece sequence in which Rick, Will and Chaka share a hallucinatory bond after ingesting psychedelic produce counts as one of the riskiest scenes ever shoved into a film of this kind, but its length and its pointlessness almost dares you to acknowledge that it existed only to provide enough off-screen time for Holly to get herself in trouble. Meanwhile, the fact that director Silberling punctuates the moment with Seals and Crofts' "Summer Breeze" – a druggy, AM-radio classic that's a personal favorite of mine – only further suggests that a sure and steady captain is at the helm, even if he's more interested in reimagining our memories of '70s kids TV than faithfully recreating the shows themselves.

Ultimately, while Land of the Lost feels like Silberling's most idiosyncratic, and daresay personal film to date (even after the introspective, semi-autobiographical Moonlight Mile), the film as a whole seems more a natural extension of the kind of comedy that is Will Ferrell's specialty – namely, the kind of meta-humor in which characters can both experience a moment, and step outside themselves to acknowledge the conventions they're either indulging or inverting. Needless to say there will be folks for whom the film's sense of self-awareness simply proves distasteful, if not offensive. But inspiring fear and loathing may actually be what this film is trying to do - which is why with or without Hunter S. Thompson, Seals and Crofts and the Sleestaks, it qualifies as the trippiest, weirdest, and all-around most unpredictable movie of the summer thus far. Whether that's a good or bad thing may come down to how you prefer your epic adventures - carefully constructed or cobbled together on the fly - but as the birthplace of the gonzo blockbuster, Land of the Lost is if nothing else an interesting place to visit.