The first book of the Sookie Stackhouse series is very similar and completely different from the True Blood (Season 1) TV show it eventually morphed into. I won't go into spoilers, both the book and the TV show feature a murder mystery, but I will discuss Sookie and Bill's relationship.
Sookie in the book comes off a bit more stable than the TV version. It could be because the book is narrated by her and so we understand more of her motivations. She's not as wishy washy as you'd think but she is way more naive than you could realize.
One of the biggest differences between the book and the TV show is that vampires in the book are suffering from a virus, so they can't help drink blood. Or that's what they want you to believe. Everyone can smell the bullshit except Sookie. When she understands that she's been having sex with a dead person instead of an infected one, she pukes. Then promptly forgets about it because Bill is so dreamy.
Bill for the most part is very unlikable, and treats Sookie like a pet. Once she finally gives in and has sex with him, that's pretty much all he wants to do. Not that Sookie complains, but sheesh. He's not as romantic as the TV version or as fleshed out. One could argue that True Blood is as much Bill's story as Sookie's (or Eric's for that matter) and you kind of miss that in the book.
Most of the secondary characters in the book are just that, secondary. We hardly know anyone outside of Sookie's immediate circle of friends and family.
All in all it was an enjoyable quick read, but you can see how the writers of True Blood really fleshed out the world and it's inhabitants.