I'm working on getting a romance novel published, so I'm seeing this from a writer's point of view as well as a reader:
- Books that shouldn't have been published. Almost any famous author can tell you about the first book or two they wrote, tried to sell, failed, and subsequently have hidden under the bed and will never see the light of day. You learn to write by writing, and that means your first book is pretty universally bad. In bygone days those books stayed under the bed, unless you got really famous and then maybe you heavily edited it and released it once you had a few dozen other books under your belt. Now aspiring authors try to shop around their first books (which they're convinced will be masterpieces), fail to sell them to major publishers, and decide to self-publish in ebook form instead.
- Related is how some smaller e-presses have sacrificed quality for quantity. They have a smaller investment in your book than they would in a printed book, so they accept anything halfway readable and hope to make up their money in volume. As a result, they cut their support for authors to bare bones: editing may be minimal, cover design is often lacking, promotional help is non-existant. And the employees who do this editing/designing are now "independent contractors" who may or may not be qualified for what they're doing. The result is a huge variating in quality for ebooks, which makes me (and other readers) hesitant about spending the money for them without first being very, very sure they're worth it.
- Authors who don't take the time to fully edit their work. This drives me nuts - too many people write "The End" and figure they're good to go. There's more to editing a book than spell check! Unfortunately, if you don't know how to check for things like pacing or point of view changes, you probably aren't doing them right.