After Sunshine and Ex Machina I'd watch anything Alex Garland wrote, let alone directed. Of everyone working in the fantastical genres (not just sci-fi), he comes up with some of the best concepts and is smart enough to relate them cinematically while not talking down to the audience.

Annihilation is probably the least accessible movie he's made, but after watching it you feel a bit like you did after the first time you saw Primer – even if you didn't fully understand what was going on you knew you were witnessing something very special.

It has that quality where a very clever writer designed and sketched out a whole universe from which (and in which) to throw his characters and write his story. The shimmer – as the inciting incident is called in the movie – has its own scientific logic that's maintained throughout, even if you can't quite grasp it at the time.

Also like Primer (Arrival is another good example), it's one of those movies you'll find yourself looking for explanations about online as soon as it's over – and it's telling that all the major movie sites have essays unpacking what it all means.

Because while it's visually splendid throughout and has some very effective images, the story is a bit harder to really dig into, and for that reason I think there'll be two kinds of responses to it – those who revisit it to fully understand it, and those who give up on it as soon as it's over, considering it impenetrable.

The beginning of the film sees an object fall to Earth from space, crashing into swampland somewhere in America where there's a lighthouse and not much else. We then meet Lena (Natalie Portman), a scientist who's husband Kane (Oscar Isaac) is a soldier frequently away on dangerous military missions, something that's hard but which Lena deals with.

Except his most recent mission was more dangerous than anything else. At the crash site, an area that exhibits mysterious properties has appeared and grown over the course of a couple of years, and Kane was in the last team to infiltrate it and try to figure out what it is and what danger it might pose. None of the other teams who've penetrated the growing shroud of multi-coloured light have ever come back, and even though Kane is the only one back from his own mission, he's a changed man.

Amidst Lena trying to figure out why he's so distant and barely human, he lapses into unconsciousness because of the dose of radiation he's received inside the shimmer. The ambulance taking them to hospital is forced off the road by government vehicles and Lena and her husband are whisked away to a top secret facility a stone's throw from the shimmer's borders where scientists try to figure out what happened to Kane.

They tell Lena he'll survive, but that it'll be a long time before he recovers. They also tell her the shimmer is slowly growing, and if the powers that be can't figure out what it is it will one day engulf the Earth. The clinical (in both senses of the word) psychologist in charge of the teams that have gone inside, Dr Ventress (Jennifer Jason Leigh) asks Lena if she herself wants to go in with an all-female team of explorers – every other team has been made up of men, so it's a shot-in-the-dark idea that maybe gender has something to do with it.

We meet the team as they get to know each other and the performances, scripted banter and easy chemistry among the leads (Gina Rodriguez and Tessa Thompson among them) elevate it above any possible hint of pulp.

Once inside, things go from unusual to outlandish to terrifying in short order. Their equipment and even their senses and memory seem to lose all track of time and direction. They're attacked by an alligator with a strange mutation, and it's not the only weird animal or plant they see.

They find a building where it seems the previous team that included Kane holed up, finding a video recording that reveals a very dark ending to the previous expedition. They're attacked in the dark by some roaring monster. Eventually the team members themselves start to exhibit strange behaviours, characteristics and emotions.

The mystery isn't neatly unrolled like a map – you only ever get clues. Radek (Tessa Thompson) realises that the shimmer refracts things – not just light, but their very DNA. It gives rise to some of the most arresting images in the movie (like the trees growing in the shape of humans) and the most eerie and terrifying (after a gigantic bear with a skull face walks into a room where one of the group has gone nuts and tied everybody else up, its vocalisations are the terrified screams of a former victim).

There are constant references to cells dividing, mutation – which the team sees all around them – and even tumours. One of the insightful essays I read online claimed the whole movie was a cancer metaphor, of the world itself getting cancer, metastasising and corrupting normal behaviours and processes as it grew.

The shimmer seems to be one huge area of spontaneous genetic engineering and splicing. When Lena reaches the epicentre of the shimmer alone at the lighthouse (it's not a spoiler – the framing device of her being debriefed by HAZMAT-suited scientists reveals early on that she's the only one left alive), she'll be met with the ultimate cypher of cell division and biological mimicry in a strange being that mirrors all her movements. We're not sure if it's a representation of the alien who first landed there, some genetic doppelganger of Lena herself, or a blend of the two.

But there's a lot more to it than just the sci-fi elements. There's a subplot about Lena's infidelity with a co-worker, and it wouldn't be there unless it had something to say about her relationship with Kane, both before and after his mission where he might not even be the same person. There are several very pivotal references to self-destruction, which Ventress is particular about distinguishing from suicide, so it's left to you to figure out how Garland considers that a theme.

It looks great and if you want to approach it like you're watching a Goya exhibition in a fever dream you'll still get a lot out of it. It's where the metaphor meets the drama, and how the lives of the characters connect with it, that's harder to get hold of. Another viewing (maybe more than one) would probably give you a few more Eureka moments, but Garland is certainly not scared to get weird and abstract.