I read all sorts of books from all sorts of publishers, but my expectations going in are different as are the kinds of books I look for.
When I purchase a book by a well-known author off a best-seller list, or a book I've heard recommended numerous times, I go into it expecting a good read. It doesn't really matter what kind of book this is so long as it's vaguely in a genre I enjoy, b/c I'm trusting the author to do a good job with it.
Am I always satisfied? No, but it's rarely bad enough that I don't finish it. These books have passed through a 'gatekeeper' and even if they aren't up my alley so to speak they meet a minimum standard.
I go into Self-Published books expecting them to be bad. Sometimes I'm proved wrong and the book is a brilliant, enjoyable read. Most of the time my expectations (of a mediocre -at-best book) prove true, I'd say 9/10 times.
But I keep reading self-published books for one primary reason -- sometimes they have fantastic ideas and new things that you've never seen before. Sometimes you run into an idea that is so original and so weird that it feels completely new to you, and perhaps "too new" for the current market. "Too different."
Those are a joy. Self-published works of short stories are also a treasure trove on occasion, if you're looking for a lot of short stories to read with a tight/specific theme. Steampunk, for example, has relatively few "professionally published" Anthologies. Venture into the world of self-publication, however, and you can find more.
But in my opinion and experience (which I realize may be not be popular), most of the self-published books out there cannot compete with professionally published ones. They just aren't good enough, unless you read so much that you've run out of everything else in your genre to check out. I know quite a few authors who think they are and blame outside factors (such as the feeling they MUST 'know someone') for their lack of success.
The other small percentage consists of books that the author self-published from the start (without trying to get through a gatekeeper) and books that are FANTASTIC but failed to get through a gatekeeper for some reason (but probably should have, because they really are good).
But for most of us, it's easier and safer to just pick up books that have been through a professional publisher, only taking risks on a specific subset of self-published novels that involve concepts/plots/characters we are interested in and can't find more of elsewhere.