At the B&N Reads blog he tagged six novels "that have been published and praised despite the fact that they’re clearly unfinished," including:
The Picnic at Hanging Rock, by Joan LindsayRead about another entry on the list.
If you’ve never heard of The Picnic at Hanging Rock, you’ve missed a novel that created a sensation upon publication, both in Australia and internationally; the film adaptation was Peter Weir’s fourth directorial effort. The story about students from an elite women’s college who disappear mysteriously during a day trip to Hanging Rock near Victoria was elevated to pop culture immortality when the publisher suggested Lindsay remove the final chapter, which explained away the mystery. As a result, the novel has no actual ending, and no way for readers to guess what happened. This is partially because Lindsay’s intended ending is quite, quite bonkers. You can read it in the posthumously published The Secret of Hanging Rock if you want, but this is one book that’s improved by a lack of ending.