I was very impressed by Slan, a fast paced, complex and filled with ideas SF novel by A. E. Van Vogt, originally serialized in 1940, then published as a novel in 1946. Perhaps unlike a lot of early SF, I think it has aged very well - it still reads pretty fresh 67 years later - not an easy feat to pull off when one is writing speculative fiction. The story is set some ways into the future (perhaps a long, long ways) as humankind has begun to evolve into a telepathic species. For along time humans, and the (possible) next step of humans of humans have been involved with trying to wipe each other out or survive. The book has a lot of layers. To some extent it's an indictment of racism. To some extent it's an argument in favor of reason, logic, learning and progress. And to some extent it's just a fun, page turning boy's adventure story with cool technology - like spaceships and atomic guns. My one disappointment is that as you approach the end of the pages, it becomes clear, there's no way the author is going to even try to wrap up all these cool threads he has been unwinding - and in a way, the book's ending feels a little arbitrary - it doesn't really reach a satisfying conclusion - but yeah, the journey there is great.