TWoP has a photo gallery up about why The Vampire Diaries is so addictive (don't they know I already wrote all those posts for you in pursuit of what makes the show awesome?), but let me save you the trouble of clicking through with these three words: the Brothers Salvatore. I like Elena, I love Bonnie, Caroline's cool, and mad props go out to my dearly (sexistly) departed ladies Vicki, Lexi, Bree, and Grams. But the Brothers Salvatore make the show. Thanks to the writing and the wily performances of Paul Wesley and Ian Somerhalder, Stefan and Damon are never who you think they are.
At first blush, Stefan's the earnest, brooding good guy and Damon's his dangerous, bad boy older brother. While Stefan can be earnest and does brood (specifically with his forehead, Damon would tell you), he's also far more dangerous than Damon could ever hope to be. Damon kills to feed or to protect himself: he's motivated entirely by his emotions. He views humans as a lesser life form, and it comes across in his every action.
Stefan, on the hand, tries to simultaneously embrace the benefits of being a vampire (longevity, super speed/hearing/strength) while rejecting that which sustains him (human blood). The wistful way he spoke of all the different jobs he's held for as long as he could didn't betray a longing to return to his human form: it spoke of someone determined to get as much as he could out of the life he chose. He's not self-loathing like Edward or Bill. He accepts, and he moves on. But you know what it takes to do as much accepting and moving on as he has? Motherfuckin' sangfroid, which he has in spades. Unlike Damon, Stefan readily forms human attachments, and his determination to protect them (not himself) from things that go bump in the night (although sadly not from Bumpits) leads him to some pretty dark places. We've seen him stake and flame-throw other vampires without hesitation. What will he do if another human ever threatens Elena? How far would he go? He's smart, funny, passionately in love, and loyal to both people and place. He's also an icy dispatcher of foes and not above poisoning his own brother. He's a study in contrasts.