Would you choose to live forever if it meant becoming ... not you? That's one of the questions posed by writer-director Alex Garland's strange sci-fi meditation on creation, destruction and mutation, which comes disguised as a monster movie.

Of course, no one familiar with Garland's previous directorial effort, Ex Machina, or his source material, Jeff VanderMeer's nigh-on-unfilmable Southern Reach Trilogy, will be surprised that Annihilation's genetic blueprint is closer to 2001: A Space Odyssey than it is to Alien. While the buildup is slow, the movie rewards viewers with a wealth of wildly creative imagery and a climax that genuinely deserves to be called "trippy."

The setup is simple. In a place identified for us only as "Area X," a meteor strikes a lighthouse, releasing a prismatic haze known as the Shimmer, which proceeds to creep slowly inland. It scrambles radio signals, and no one who ventures into it returns — well, almost no one.

We learn all this along with Lena (Natalie Portman), a biology professor whose husband (Oscar Isaac) disappeared on a classified military mission into the Shimmer. After he mysteriously returns almost a year later — incoherent, and near death from organ failure — Lena feels compelled to explore Area X herself.

She volunteers for a new government mission led by the icy Dr. Ventress (Jennifer Jason Leigh). Together with a no-nonsense paramedic (Gina Rodriguez), a geologist (Tuva Novotny) and a physicist (Tessa Thompson), they venture into the unknown. Within the Shimmer, the women find a sinister Eden of weird flora and fauna, organisms that appear to embody impossible mashups of different species.

Owing to a framing narrative, we already know the mission won't go well. Through sometimes-clumsy flashbacks and exposition, Garland's script spells it out for us: These are five wounded, self-destructive characters facing an existential threat. Who will stand firm, and who will succumb?

Or ... does it matter? What does it mean to "exist," anyway? Those questions increasingly dominate as the story itself goes into uncharted territory.

There's a certain hoariness to the doomed-mission scenario and a remoteness to these characters that keeps Annihilation from achieving the emotional resonance of, say, Arrival. While Portman is moody enough, she doesn't bring immediacy to Lena's conflicts, and Garland's portentous screenplay tells more than it shows.

But when the film finally starts unveiling the Shimmer's effects on human beings, it goes to such rich and strange places, both narratively and visually, that it mesmerizes despite its flaws. Memories of old episodes of "The X-Files" fade as we gaze on images as appropriate to a Grimm fairy tale as to a sci-fi thriller.

Area X's hypnotic theme-park pastels (courtesy of cinematographer Rob Hardy) conceal tableaux of fascinating, horrifying grotesquerie. While the movie does have scenes of body horror and physical abominations run amok, its mood can shift on a dime from terror to elegy. Where some observers see "annihilation" in the Shimmer, others see something less clearly destructive: refraction. It's a visual and thematic motif that Garland introduces early, in a shot of entwined hands seen through a water glass, and works into an unforgettable climax.

At its best, Annihilation is heady experimental cinema with "future cult classic" written all over it. At its worst, it drags a little, torn between marketable Hollywood horror movie tropes and terror of a more elemental kind. By the end, though, the best parts of this cinematic chimera dominate. It's a must-see for anyone who loves the truly speculative side of science fiction.