@Thomask Kizumonogatari is exciting. Multiple voices too.
I'm listening to a really bland Japanese Novel Audiobook in English now, Death by Water. 16 hours of a monotone man trying to slowly voice old characters talking about past events over and over again to try and write a novel + play. Doesn't help that the audio is too low on my phone (I don't like headphones). T.T
I did get finished with a single person talking in a more monotone (not so varied at least) voice in Malice, but that I could stand that more since it was shorter and basically a recording of events in a case study on a criminal.
Monotone can be ok, as long as the inflections are correct. I've had one or two where they were terrible. As in nearly non-existent.
Keep in mind, I've only listened to a handful of audiobooks over the years, alot of 'self help' stuff that was more of a seminar setting, but still, when audiobooks push you to seminar stuff, you know its rough.
I listened to a series called "Left Behind" audio drama a few years ago, now THAT was entertaining. You could close your eyes, and nearly imagine it playing out on the TV in front of you.