That depends on who you talk to, of course.
The self publishing boom has given rise to the publication of millions of new books, the majority of which would never have been published traditionally because they would be either deemed to be of insufficient interest to return a profit to the publishers or because they were, frankly, just too terrible to see the light of day.
How good a book is can be very subjective in many ways, but certain rules must apply.
If you buy a traditionally published book, you may be reasonably certain that it has been edited and proof-read to a high standard, the printing and layout of the book is of good quality, and the actual contents – plot, dialogue, character development et al – are sufficiently well written as to repay your reading time.
There are no such guarantees with a self published book.
As a member of several Goodreads groups, I receive regular emails which consist largely of other members promoting their books. These promotions frequently consist of a synopsis of the book, extracts, and links. All well and good, but the number of extracts that are poorly written, unedited (it would seem), with poor print layout, and the number of synopses that are equally poor, is very high indeed. Probably the majority, unfortunately. And should I follow the link to the ebook sales site and read a longer extract, frequently this, too, is filled with more of the same errors.
As far as the plot and dialogue and all that goes with that is concerned, I admit that may be partly down to taste. I have no doubt that some poorly written and poorly plotted books still give great pleasure to many readers, and good luck to them. There are certainly examples of the same amongst traditionally published books. And styles go in and out of fashion, anyway.
What I do take issue with, though, is poor, sloppy editing.
Most people cannot afford to pay for professional editing – I certainly can’t. I understand that. It means doing the job yourself, but taking infinite time and care over it. Check it over and over again until it is the best you can do. The odd mistake will slip through, but that happens even in a professionally edited work. Persuade others to act as beta readers for you. They may not be professionals, but they will spot things you don’t. You are too close to the work, anyway.
If you can’t do that, don’t publish the book.
Let’s take layout first. It only takes a careful look at half a dozen professionally published books to get a good idea of what that layout should look like. And you can buy books that supply more detail. If you are serious about your book, you should do that.
Spellcheck is a useful tool, but only if it is used properly. It recognises a correctly spelled word in its database, but has nothing to say about the suitability of its use. I do find it particularly irritating to come across passages where the completely wrong word has been used, no doubt because Spellcheck flagged it up as the correct spelling. Common examples are groyne / groin, sheer / shear, alter / altar etc. etc. etc.
Grammar is the biggest minefield, though. We all get that wrong at times, even the best of us. But at least avoid the biggest howlers – the so-called grocer’s apostrophe, for example. Put the manuscript through a program such as Grammarly, which is free to download, to pick up the majority of the errors.
Another phenomenon I have seen recently is a 4,000 word story published on Amazon as a ‘Novella’. I suppose there’s nothing wrong with selling a story that length, but anything that comes in at 4,000 words is a short story. And quite a short one at that. To describe it as a novella, no matter what price it is being sold at is, quite frankly, a bit of a bloody cheek.
Please don’t do that.
And I’m sure many other readers have their own pet peeves.