I've also enjoyed books read by their authors. I've listened to books read by John Crowley, Junot Diaz, and Richard Dawkins for example. Without exception they were effective, and Diaz did some brilliant accents. Perhaps an author is so well entered into his or her words that they don't need to be specially trained to make the book live.
The three where the reading spoiled the story were read by people without modern voice training, who were also not the authors. This is Water by David Foster Wallace was read by his wife, as he had died. I also listened to a fairly poor autobiography of a criminal psychologist (Helen Morrison) - she read her 'own' words, but the book had been ghost-written for her, and you could tell by the clumsy way she read the sentences, not knowing where to put the stresses.
And the third book, which I have come to a halt mid-way through this week, is The Lodger by Marie Belloc Lowndes. I think it's an old recording, made many years ago. The book is set in Jack the Ripper's London, so the characters are lower class cockney types. The reader is a cultivated American lady. This is absolutely not a criticism 'Americans can't do British accents'. Most can, some brilliantly. I think however this recording was made before modern communications made it commonplace for us to converse internationally, and before modern voice coaching was in place. She mixes up lots of different accents, such as Yorkshire vowels and Cockney inflections. Honestly, it makes Dick Van Dyke sound like Meryl Streep.
But anyway - only three failures in three years isn't bad is it? I certainly would continue to get books read by their authors, and books read by modern trained actors are always well delivered.