From the introduction:
Why Upgrade to 1.5?
What, you mean you want reasons other than us
just plaintively saying “please”” Of course you
do, and this book is full of those reasons.
Just like with the main book, Now What? has not
only been completely rewritten, it’s also been
expanded. While many of the ideas in this book will
sound familiar to those that have read the original
first edition, we’ve gone through every rule, every
change, every idea and expanded them, creating
new refinements, new ways to play.
Plus, we have so many more ideas that we had
to implement, new things for the GODs to create,
new ideas on what to throw at your players, and
just so many answers to questions we received
from players and GODs alike that, well, this book
is just so vastly different from what came before
you’re going to want it if you have any desire to
run a game.