I've only seen the first two seasons of True Blood, but I know season three will introduce werewolves and fairies (or fair folk). However, at this point it's clear to me that the show appeals to different people for different reasons...

Right off the bat, there's the matter of sex. The series is overflowing with weird, funny, romantic, and disturbing sexual encounters (and since it's on HBO, the scenes are pretty graphic and get away with things you might not see in a regular TV series or in a film). Then you have, along similar lines, the violence. The series is pretty bloody and gory at times.

Another aspect of the show's appeal, especially with the first two seasons, is the way that supernatural beings are used as an allegory for the outcasts in our own society (whether they're outcasts because of race, gender, sexual preference, or otherwise). I think that the use of political and social commentary, while somewhat juvenile, is pretty effective and that much like X-Men lures people in who feel like outsiders.

For me, the appeal of the series is two-fold. Firstly, I love the way that they've used mythology and updated it for contemporary issues (vampire blood as a drug was a nice touch as was the fairy telepathy for Sookie). Secondly, the characters are wonderfully refreshing and well-acted.

I've seen all three seasons on HBO (and several eps more than once) I'm not sure what the appeal is to others; I originally came for the vampires, but stayed for the characters. I'd watch the show for Sam and Lafayette even if Bill and Sookie took off on a long honeymoon. I kinda wish they would, actually....

Season 1 was enough to get me hooked with the introduction of the primary conflicts, both on the personal level and sociologically.

Season 2 had some wonderful moments. The Fellowship of the Sun and their anti-vampire evangelical mania was a delightful parody of everything that makes my skin crawl with regards to religious extremism. The conclusion of that arc with the too-brief appearance of the quietly spiritual Godrik, Eric's 3,000 yr old Maker, made a nice contrast to the hate-based Fellowship. The Maryann/Tara subplot seemed to drag on, but development of the Hoyt and Jessica's relationship was (and is) simply adorable.

It almost seems like Season 3 tried too hard, with a frenetic pace and the addition of almost too many new subplots and characters. I don't want to give up any spoilers since Season 3 hasn't been released on DVD yet, but "Werewolves and Faeries and Shifters, oh my!" Also completely demented, psychotic vampire characters which were just too much fun. (And psychosis seems like kind of a natural outcome for some of those cursed with immortality, doesn't it?)

For me, while I do love the social commentary and the humor, the characters are what have kept me coming back.