I think that the Sam thing has been signposted right through the series to be honest - in almost every book they've almost got it on but been disturbed, or had a 'moment'. He was her most loyal and steadfast friend throughout, and always had her best interests at heart, as opposed to the vampires who by their nature are twisty, manipulative, possessive and self-serving.
I hadn't enjoyed the last two or three nearly as much as the early ones but I thought that this one was quite good. Let's face it, the series was never high literature, was it! Still, I think Sookie was a fantastic character and it's been really interesting to see how she's matured and changed through the series, especially how all the violence has hardened her but not eroded her goodness.
I loved all the vampire characters and especially enjoyed it when she got it on with Eric, but it was the will-they-won't-they that was a lot more exciting than the actual relationship. i always saw that coming to an end. I also think that it would have been going against everything Sookie believed in and held dear for her to have become a vampire. And if she didn't - how was that relationship going to turn out?? Sookie wanted children, family, sunshine, humanity.
I think that the people getting hysterical over her not ending up with Eric are a bit bonkers, frankly - as if they have the right to control what an author writes just because they like (are obsessed by, in some cases) the series.