"Audio was Bad"
The content is good; I read the Kindle version while listening. Well, I tried to anyway. I had to give up on the audio because of an annoying sound running through at least 1/2 of the audio version. In addition, the volume of the narrator's voice was difficult to modulate without it being either too loud to comfortably listen or too low to understand.
"Decent Content, Awful Performance"
The book had pretty content, though it probably could have been 1/2 its length and conveyed the same ideas.
The performance of the narrator was terrible. It seemed clear that he had little knowledge of the subject and simply read the words in a boring monotone fashion. In addition, though I don't have a copy of the written book, I'm pretty sure he frequently said the wrong words and also mispronounced words often.
"Excellent"
This was a very good book, but if you're looking for just one Voltaire book, I'd go with Candide over Zadig.
"Not worth your time or money"
As others have said this book is basically the random opinions of a middle aged man that fancies himself an expert on just about everything.