Big fan here! I read all of the books (they have definitely gone downhill IMO) and watched all the episodes.
I L O V E what they've done with Lafayette, and to a lesser degree Tara, Jason, Jessica... basically all the minor characters. Russel is pretty great, so was Franklin.
I DO NOT love what they've done with Eric. In the show, he is so dark and brooding and WEEPY and kinda angry lol. In the books he has his negative moments but for the most part he is lighter, mischievous and more social. He flirts more. I hope we get to see that in the show.
I think the only time we've really seen the Book Eric is when he tricks her into sucking the bullet out of his chest. That, and the tone of the scene, is much more book-like. Alan Ball said in one interview that Bill and Sookie will be the core of the show, which would explain why we see so little of Eric. It's a shame, because Book Eric is a great character.
This is who inspired Eric, BTW:
Personally I think Skarsgard is fine (I wish he would stand up straight though! And preferably stop slicking his hair back).