I was talking to someone recently about my book situation. I have one book. But I'm writing a second. And aside from the fact that the setting is essentially the same, the stories are vastly different.

This person (I forgot who it was I was talking to, now) was rather astonished that I wanted to put my first book away for a while. And I was at a loss to explain just why it wasn't right to see the light of day.

I found a neat little article by David Dvorkin (a sci-fi/fantasy/Trek writer), and a section that summed it up perfectly for me:

The first book is different from all the subsequent ones, and not just in the way that one's first sexual experience is different from all the subsequent ones. Normally, when a writer writes his first book, he's young and filled with enthusiasm, with the delight of manipulating words and characters, with the certainty that this book will take the world by storm and bring him fame and fortune. Along the way, he'll also teach the rest of mankind lots of important stuff about life and human nature and politics and whatever else he's thrown into the book. First novels tend to have a whole lotta stuff in 'em. That's partly because our young writer has learned so much about everything in his twenty-something years, and it's partly because he hasn't yet learned to cut out what he sees as brilliant discursions and editors recognize as fat.

Not to say that everyone is like this, but for me... well, that's just perfect. :)

So yeah. That explains it. If you want to read the whole essay, it's here.