Putting your work up to be either ignored or judged is a different sort of challenge, but not unique to self-publishing.
One thing which is almost guaranteed to come along with the decision to self-publish are two words: Needs Editing.
Rather too many self-publishers type their books out and throw them up raw. Some self-edit. Some crowd-source or trade editing with other writers. Some hire editors, and make sure to list those editors up front and central in the book's metadata. Sometimes those editors will be capable and talented people, and sometimes (as apparently was the case with Amanda Hocking's hired editors) not so much.
The copy-editing side of this process - eliminating typos and grammar errors and spotting continuity issues - is relatively straightforward (though even then you will find yourself coming up against grammar myths or "spelling errors" based on British/US/Australian English differences). But it's fairly easy to say that a book has few spelling or grammar issues.*
Developmental editing - consistency of characterisation, issues with pace, recommending changing point of view, boosting the role of a character, gender-flipping the protagonist, or even altering how the book ends to produce a satisfying and powerful reading experience - all those are a little less definitive.
A developmental editor is a highly experienced reader who can push you into seeing how to make your book even better. In their view.
Here are two reader views of the opening of Stray.
Love love loved the beginning survivalist part! And the worldbuilding was incredible, though I think some of the humor I liked so much, as well as the characterization, got a bit lost in the last half. - Wendy Darling
I really enjoyed this book. It was slow going to get into it but I'm glad I stuck it out. The story picks up momentum almost imperceptibly and after about 100 pages becomes 'unputdownable'. - Laura (Kyahgirl)So which editor did I get? The one who thought that beginning survivalist part was brilliant, and wanted more like it, or the one who thought that part was dull, and fell in love with the book later on?
No book is the same from one reader to the next. No editor can polish your book to be "perfect". Experience and personal taste will combine to produce advice which will please some of the people some of the time, and maybe even lots of people most of the time, but never ever all of the people all of the time.
This isn't a suggestion to not use editors. Feedback on your writing is incredibly valuable, allowing you to see the book through different eyes. But no matter how much editing your books have gone through, you will not please all of the people all of the time, and because you're self-published you will be told that your books Need Editing.
This will be un-fun at times, and possibly the person saying that is simply not one of "your readers", far more interested in action than character development, or vice versa, but it's also useful free feedback, giving you more things to look for when your next novel is going through the editing rounds.
I'll finish this off with two quotes from Diana Wynne Jones about editing. First a positive one:
On the good side, there are enormously high standards. None of the editors I have worked with would have accepted much in the way of clichés. None of them have ever let me get away with any muddle in any plot, nor with any factual inaccuracy; and though some have queried things that struck them as peculiar, they have always been delighted by originality. This naturally has put me on my mettle. Knowing that everything I wrote was going to be subjected to extreme and shrewd scrutiny, I take pains to get the finished manuscript right, if I can.
Then a cautionary one:
I hate being edited, because my second draft is as careful as I can get it. I try to get it absolutely mistake-free, and absolutely as I feel the book needs to be. Then some editor comes along and says, 'Change Chapter Eight to Chapter Five, take a huge lump out of Chapter Nine, and let's cut Chapter One altogether.' And you think, No, I'm going to hit the ceiling any moment. Then I call for my agent before I get my hands round this person's throat.An editor can be a very useful person to have on your side. But they're not a magical guarantee of perfection, and they're not unique to trade publishing. Always listen to, then weigh and evaluate any feedback on your writing. And don't let the 'slings and arrows' get you down. A small press editor once told me that it simply wasn't possible for a self-published book to be as good as a trade published book, but I've yet to hear a believable argument as to why this should be.
Editors were very majestic in the days when I first started writing. There was one who got hold of The Ogre Downstairs, and rewrote the ending entirely in her own purple prose, which was not in the least like mine, and I decided I was going to change publishers. 'No, no, no,' said my agent. 'You mustn't do that. Carry on and see if you can manage to persuade her.' And of course I couldn't persuade her. And then Charmed Life: I know by the time I'd done the second draft it was absolutely perfect, it really, really was, I mean just as it is at this moment, you know. And this woman rang me up and wrote to me and told me exactly this sort of thing: 'You must take out this chunk and that chunk and rewrite this and alter that,' and I was furious. And I thought surely we can do something about this. And thank God it was the days before computers. I said, 'Send me the typescript back and I'll see what I can do.' So she did, and I cut out the bits she told me to alter, in irregular jagged shapes, then stuck them back in exactly the same place with Sellotape, only crooked, so it looked as if I'd taken pieces out and put new pieces in. And then I sent it back to her, and she rang up and said, 'Oh, your alterations have made such a difference.' And I thought, 'Right! Hereafter I will take no notice of anybody who tries to edit my books.' And I don't, I make a frightful fuss if anybody tries to, now. - Reflections on the Magic of Writing.
* I've never put a book out which didn't have a typo (still waiting for someone to spot one in And All the Stars, but it's sure to come), but I'm at around 99.5% correct and aiming for better.