It was the atmosphere - cold enough to have me reach for a scarf, a sense of dislocation, and dirt beneath my fingernails - that impacted most strongly for me. Along with a cast of characters so much, and so often at odds with each other that it didn't feel like fiction.
John Wyndham's 'Chrysalids' had a huge impact on me, as did Robert Heinlein's 'Farnham's Freehold'. both of which I read back in the 1980s; I suspect this will join their ranks, despite the need for an occasional rant at Alice's subordination to 'the men' and wondering at their inexplicable reluctance to venture further afield. [It was paperback I read]