Last And First Men, by Olaf Stapledon
A fictional history of humanity, from beginning to end, across two billion years.
This is one of the few truly original and novel novels I've ever read, it's so excellent and I'm sad I didn't book-thought it when I read it because now I remember very little of it.
However, the big picture idea is that 1) it's a big-big-picture history of humanity (written in the far distant future), and therefore 2) its scope of interest is only the biggest-picture events and trends that truly matter on civilisational timescales, and 3a) therefore has almost no individual characters, and 2b) none of the usual narrative devices we're used to -- civilisations rise and fall, sometimes falling to great great lows, things cause other things in sometimes unexpected ways, and there isn't the usual feeling of A Story unfolding but rather a kind of patchwork quilt emerging. (If you've ever seen Koyaanisqatsi, it's in some ways reminiscent of that).
The upshot is forcing you (the reader) to really think about what (might) matter on a civilisational/universal scale, and the ways in which our individual human minds (and presumptions about our own species) might be limiting and limited. As the preface says, we should "familiarise ourselves with the certainty that many of our most cherished ideals would seem puerile to more developed minds." It really is magesterial and brilliant and amazing that Stapledon pulled it off -- I don't remember if it was always interesting, but the fact that he managed to sustain my interest at all is kind of miraculous.
Interesting fact-oid: the foreword advises you to skip the first four sections of the book, which I appreciated and then did.
Also interesting: in some way I no longer remember, it was mentioned somewhere that Stapledon influenced (and was promoted by) Doris Lessing.