And unlike most hard sci fi: it's optimistic, the characters are vivid and memorable well after you stop reading, and i've never read anything else like it. Except maybe Ursula K Le Guin's The Disposessed (and she was his mentor).
[0]: https://imafungus.pensoft.net/article/145477/
Edit: no disrespect intended to the author, who was likely unaware of such an amazing trilogy. I am just very excited about lichen on mars. Far, far, far more excited than I am about humans on it.