A neglected series is Riverworld by Philip Jose Farmer. There are five volumes that are a great read.

All humanity is resurrected after death on the banks of a strange river. Each book deals with a real historical figure and the struggle to understand the mysteries of Riverworld. Each volume more or less follows characters from history (Richard Burton, Mark Twain, Cyrano de Bergerac and others) who embark on a journey to travel to the end of the River in order to solve the mystery of their resurrection. It's quite pulpy but very enjoyable.