I just recently purchased this book mainly because of a new novel I finished. It brought up an interest in the Yuan-Ti. I've been waiting for this book, Serpent Kingdoms, to come out so I could insorporate them into a campaign.
Yes, this book does have a lot of story. it is meant for DMs with imaginations to carry the story on into their campaigns, or even to start a campaign. I believe that was the purpose of this book. It gives an impressively large background on the different races of serpentlike beings. It does have a new monsters for the Dm to use, new feats that concern those new monsters (hint hint, not for the player), and it provides many different sites for the DM to use.
I say if you don't like the purpose and usability of this book, give it away. You're not hurting anyone but yourself as a DM. Even players can use this book. I, as a DM, will allow my players to use a few of the new monsters, or even the old ones now, as a player race.
All in all, this book is excellent for working into an ongoing campaign, or even to start up a new one. Create a new world with this book even (humans, elves, dwarves...slaves? sounds fun to me). I recommend this book to any DM who has given thought to using the serpent races more often in their worlds and to any DM is stuck with writing a new campaign. Players, check it out as well. Just remember to keep player knowledge from character knowledge. Have fun gaming!