(Plenty of other people have praised this, and the trilogy it concludes, since VanderMeer published it in 2014, and I've generally liked VanderMeer's work - so it's more than likely the issue is with me.)
VanderMeer famously put out this entire trilogy in less than a year, but it took me more than a decade to get to it: first Annihilation, then Authority, and finally the conclusion. They're near-future, or maybe alternate-present, horror-tinged science fiction. Something transformed a stretch of coast - VanderMeer never says in the text precisely where it is, but it was inspired by the St. Marks National Wildlife Refuge in the Florida panhandle - about thirty years before. Area X is full of strangeness, and wiped clean of nearly all signs of humanity. A government agency, "Central," established a division, the Southern Reach, to investigate Area X; it has sent expeditions through the one portal into this transformed landscape regularly over the decades, with minimal scientific results and various horrific ends to many of the people involved.
Annihilation was the story of the "twelfth" expedition - like many things about Area X and the Southern Reach, the initial story is not precisely true - told by "the biologist" through her journals. Authority was the story of a new Director of the Southern Reach, sent by Central after a failed career doing other spy things elsewhere in the world, who was generally just called Control. He spent a lot of time talking to a version of the biologist from the first book, created by Area X and called Ghost Bird for opaque reasons, and some time countering various bureaucratic maneuverings and schemes from longer-serving members of the Southern Reach, with their own agendas.
Acceptance is a direct sequel to Authority - Control and Ghost Bird went through a portal to Area X at the end of that book, and one narrative strand here follows them. It's also a prequel to the whole series, with a major thread about Saul Evans - the only major character regularly referred to by his actual name in the novel - the keeper of the lighthouse that eventually became a focal point of Area X and the only major human-made piece of infrastructure remaining there.
VanderMeer rotates viewpoints - from The Lighthouse Keeper to Ghost Bird to Control to The Director (another major character from the earlier novels, who I've neglected to mention, who also has two names) - and switches timeframes, covering the period just before the creation of Area X with Saul, various times during the Director's tenure running Southern Reach, and the journeys of Control and Ghost Bird back in Area X.
I found each of these threads to be separate from each other, part of the same overall story of Area X but not as resonant with each other as I think I was supposed to. In particular, Saul's story was just sad and pointless: he was manipulated by other people, and maybe the mysterious cosmic or alien forces behind the transformation, so he lost everything and was utterly destroyed in a horrible, unpleasant, creepy way. So, yes: he was mostly happy, and had a man he loved, but then something used him to transform the world, kill millions of people, and bring about Creepy Armageddon. I didn't find that cathartic, or inevitable - just tedious and unpleasant and utterly regrettable.
This was the kind of book where I liked the sentences and paragraphs, appreciated the character insights and wanted to know how it all worked out - but didn't care, in the end. This is a world that has had a Weird Apocalypse, and we still, after three novels, don't know how or why. There's only so much wandering around and talking about different pieces of the elephant I can stand without an actual elephant being revealed. And, I suppose, I've discovered that's two novels worth: I can take two, but three is Right Out.
You may react differently, but, if you've read the first two Southern Reach books and are hoping for a big reveal at the end...well, you may want to recalibrate your expectations.
