Olaf Stapledon isn't afraid to work on a big canvas. His "Star Maker" spans the life of our universe and beyond. Rather than searching for power, or money, or fame, or even love, the main character in "Star Maker" roams the universe trying to become aware enough to perceive and interact with a higher power. It's a spiritual book in which the universe is revealed to be both sublimely ordered and painfully uncaring. In this epic and amazing work, the life of humanity is a but a single thread, a few paragraphs in the larger story.
"Last and First Men" is more tightly focused, and follows the development of humanity over the course of some three trillion years. It starts in our own time, and moves forward slowly at first. As is inevitable, Stapledon's ideas about the immediate future date the work, but once modern civilization is safely past, the book hits its stride. Eighteen species of humanity come and go, rising to meet the challenges presented by the universe around them (or succumbing to them). Along the way, Stapledon explores ideas about longevity, higher consciousness, the proper goals of a world society, and imagines that larger patterns of rise and fall (for the world, for the species, for intelligent life in our solar system) might lie far beyond our own history.
The focus of "Last and First Men" is societies, states, civilizations, and species rather than individual lives. It's only toward the end that we learn the history of the narrator and find the full spiritual center of the book. "Star Maker" on the other hand, begins with the life of an individual and his core quest, and draws us in from the beginning. The later book ("Star Maker") seems more mature and complete as a result. I tend to pick lovingly worn second-hand copies of books in used bookstores, which doesn't always lend itself to reading things in the right order. In this case, I read "Star Maker" (the sequel) some months before "Last and First Men". "Last and First Men" holds up well, but if you get the chance, go through them in order, as the ideals of "Last and First Men" are expanded and played out on an even grander stage in "Star Maker".
Both "Star Maker" and "Last and First Men" are highly recommended food for the mind. If you find yourself getting a headache from the ultra-wide focus of both books, you could do a lot worse than Larry Niven's "World Out of Time", in which a single individual encounters the distant future (in two discrete chunks). I'd also recommend "Forever Free", by Joe Haldeman, which pans out toward the end to embrace some of the same scope, but keeps its focus more firmly on the individual.
Yet again I'm indebted to the Sci-fi Masterworks series for broadening my horizons to include Stapledon. Stay tuned for the few remaining installments ("Tau Zero" is coming with me on my next trip).