Does any writer ever feel a book is completely finished? Or it simply that deadlines must be met and the book turned in, whether or not you're happy with it?
In rereading some older books, books I thought were pretty danged good, I'm seized with an almost irrepressible urge to rewrite them, sentence by sentence. I've rationalized this scary feeling by telling myself that I'm a better writer now, that I never cease learning with each new book, and it's okay, take a deep breath, and move on. But it's not that easy.
Self-doubt about one's artistic ability seems to be inherent in the creative process. You don't improve if you think you're God's literary gift to the world. But I've countered that paralyzing demon so far by knowing that my talent isn't "mine," in other words, a personal possession. I can never explain where my ideas originate or how I express them, because I know they come from a source other than my pea-picking teeny brain. I can, and do, work on my craft. I study other writers and their techniques. I work to make the story clear and fun to read. But those are just mechanics.
As a creative person, I'm a work in progress and I don't intend to stop learning for one second how to be better at what I do.