Sometimes musicians are inspired, and sometimes they overplay the same riff to an audience that nods indulgently as they already know the next note.
Sometimes authors do the same thing.
Zechariah Sitchin is an author whose early work intrigued me, even if it didn't really convince me. Sitchin built his career around the premise that the Sumerian and Hebrew gods were really alien beings who came to Earth to reshape our planet; that the tales of the Torah and the Enuma Elis were actually human retelling of alien conflicts; and that much of early Middle Eastern culture developed due to direct alien intervention. Sure, it's Erich Von Daniken territory, but he pulled it off with a clever blend of innovative interpretations of seldom-referenced Sumerian myths and insightful looks at archeology, anthropology, and history.
The problem is, Sitchin became so popular with a devoted group of readers that what started off as clever, insightful "speculative quasi-history" deteriorated into the literary equivalent of playing the same riffs to an audience already overly familiar with every note. In his latest book, The End of Days, Sitchin no longer tries to sell his ideas to new readers; instead, he's going through the motions, referencing his own works and repackaging his old ideas for a readership overly familiar with the concepts. I once was intrigued and amused; now I'm bored, and I think that Sitchin is, too.
I still recommend his early books for readers who can enjoy this sort of far-reaching fantastic reinterpretation of history and mythology... but I can't recommend this book at all, even to his fans.