Dune (and the sequels through God Emperor).

I’ve never found a writer who could discuss humanity writ large — both in masses, and over enormous spans of time — like Herbert. Dune is the easy to read, fast moving approachable yarn that gets you in. The real masterpiece is God Emperor, where we get to see humanity over thousands of years, and we really learn Herbert’s most important lesson: beware the charismatic dictator.