Your first line needs to be everything. You know that. But did you know that your last line is, essentially the yang to the first line's ying?
The last thing any reader is going to see of your book, is going to be the last line. It has to satisfy them because there's nothing else after that. It needs to be memorable, special and definitely not cheesy. It needs to match the everything of your first sentence. It needs to balance out.
I mean, if a book were a sandwich, you wouldn't put one slice of baked-from-scratch-bread on top (the first line), mouthwatering-pick-your-favorite-fillings in the middle (your story) and dry-left-out-on-the-counter-too-long-store-bought-bread on the bottom. It just doesn't make sense.
When I'm browsing books in the store I always look at covers first (Yeah, I know that's shallow), then I skim the first lines but, because there's so much pressure on them, usually these are good. Finally, I read the last line. And, honestly, a lot of them suck, or are cheesy, or are interchangeable (they could end any story). That definitely makes me question what's in the middle. It makes me doubt the writer and if someone hasn't promised me the book is worth my time I will never read that book.
It all really comes down to this, I think your last line says more about what kind of writer you are then your first.
Maybe that's just my opinion but, when you look at your manuscript, at the journey your readers will go through, I want you to look at your last line. Was the journey worth it?
The real question is this: how do you want to leave your readers?
Thoughts on the last line? Do you ever read a last line before you start? Are you proud of your last line? Any other thing in writing books that is so important but you think get's overlooked?