First off, a book is rarely “finished.” It’s just that various factors weigh in to make you stop fiddle-farting around with it. Second, never ask anyone who’s just finished a book if they’re happy with it, because the answer is always IT’S AWFUL MY CAREER IS OVER GET AWAY FROM ME I WILL TEAR YOUR FUCKING HEART OUT AND EAT IT IN FRONT OF YOU. There’s a terrible space between the conclusion of the copy-editing and the release of the thing where you’re convinced that it’s a rotten piece of work and you’re going to be Found Out and everything is over. You start telling the wall — because you don’t know anybody any more, because you’ve been indoors for months destroying a laptop with your crap — that if you only had another six months, if you could just alter a couple of things, if you could just maybe take out and replace a plotline, and maybe the main plot, and all the characters, and change the title, and write a whole different book, then everything would be fine.
You won’t start liking it again until six months after your “friends” have helpfully forwarded you all the bad reviews. You come out from under your bed muttering “…wait, what? Did they even read the fucking thing?” And, as this delusion of competence takes hold, you start thinking about writing another book, having completely forgotten everything in the first paragraph.