One thing I'm finding while writing through Nanowrimo is that all the major structural flaws are suddenly very obvious.
Beginnings: I know through my first six chapters that I have not nailed the beginning. I've heard one suggestion before: to flip the first and second chapter, or at least to put the second chapter first and build chapter one in as backstory later. And this would probably help. But that will be a problem to solve during revisions. I think my "right" beginning is in those first six chapters somewhere, so that is good news. But I'm amazed at how obvious it is when you write quickly that what you have probably is not quite "right". But you do it anyway.
Middles: Have you ever heard the term "The Sagging Middle"? I'd like to find one Nanowrimo writer who does not know what I'm talking about. Just one. But writing through that sagging middle, pushing ourselves to keep going even when it feels like it's one monotonous, never-ending death sentence for our books...and eventually finding the excitement again: that's what makes us real champions.
Endings: Do you ever feel like ALL you can think about is the damn ending? When will I get there? It's going to be great, right? It HAS to be great after all this.
Yes, I'm not even 20k into my story and all I can think about is the ending. Pretty sad, isn't it? But that's just today. Tomorrow will be better. How's Nano going for everyone else?