Tuan, my respect is equal for self-published and traditionally published books, with the same criteria in both instances; to learn, enjoy, and hopefully, find inspiration. In some cases, reproduction quality might be a major consideration. Among my favorite photo books are a few self-published gems that would likely lack the audience and return expected of a traditionally published book.

Self-publishing often concerns different goals and expectations. I published a book to tell my story of six decades as a fine art photographer, with glimpses of a bygone era. I anticipated a small audience and chose a publisher of high reputation. He agreed to print my text and photographs following my layout, and was on press. Reproduction quality was a major consideration. The resulting book represents the necessary rapport of photographer and publisher.

As others have noted, traditionally published books are no guarantee of quality, nor self-published books of lacking same. It's not an easy question!