This is the story of Clare and Henry. Henry has a genetic condition that throws him forward and back through time, uncontrollably and without warning. Clare is his lover.
The novel skips backwards and forwards through time. Some people find this annoying, but I think it reflects and allows us to share in Henry's experience of skipping through time, and it allows Niffenegger to play some clever tricks on the reader, revealing details and explaining things that you read earlier as the novel progresses, so by the end you have a full picture built up like a jigsaw puzzle.
I also found the way Niffenegger kept referring to creating things - art, poetry, children - interesting: trying to create some stability in the face of the chaos of time's movement. The novel asks searching questions about destiny - do we have free will if the past cannot be changed? Is everything predestined? It is about love and loss, and "world enough and time". It can be funny, and it can be elegiac. It is beautiful and tragic and sometimes desperately sad - I wept at the end, although I liked the note of hope, how Henry kept coming back to his family, how, as Alba said, he wasn't continuously dead.
And I like the magic realism aspect - technically, it is SF, but it doesn't feel like SF. It isn't about the idea of time travel, although this is explored magnificently, but about the characters' experience of it, what it feels like to be the one going or the one waiting and wondering. I can't think of any imperfection. It's wonderful. And the film is surprisingly true to the book. A bonus, because I love that, too.