I came across the following quote from the poet, novelist and critic Randall Jarrell:
…a novel is a prose narrative of some length that has something wrong with it…
(From The Unread Book, which I can’t find a link to anywhere.)
I found this strangely encouraging. I suppose the trick is to make sure it has exactly the right thing wrong with it…
ninevoices 
I suppose War and Peace does bang on a bit in places, but it was written to be read (and discussed) by folk in candlelit rooms through a long, dark winter, so it needed to be meaty. But I would struggle to find ANYTHING wrong with Pride and Prejudice, or with The Gruffalo. Though the latter isn’t a proper novel, is it? Just a wondrous story.