After finishing the second season of Supernatural, I think I have figured out why I like it so much. The world of the occult, zombies, vampires, demons, magik (not a typo), etc. has been so inherently European in the past. I can only think of the terrible "John Carpenter's Vampires", "Lost Boys" (to some extent), and maybe some aspects of Buffy being more American takes on the subject matter (although all the examples are very vampire related).
Supernatural is like a real grade A American take on the occult. Muscle cars, check. Hard Rock, check. Cowboys, check. Hot chicks, check. Big guns, check. The way that Eric Kripke and Robert Singer have managed to work things like Samuel Colt into the mythology of the show gives it a very American feel, which gives everything a fresh feel. Mix in Buffy-esque humor, intelligent homages, and some general ass kicking you have a winning formula.
I applaud the show for putting what seems like a definitive stamp on the yellow eyed demon plot line that has been dangling throughout season 1 and 2, and not leaving us with a big cliffhanger. While the 2-part finale was tense and exciting, it almost felt anti-climactic by the end of it. I did really enjoy the short return of Papa Winchester, played excellently by Jeffrey Dean Morgan (yes that dude who was on Grey's Anatomy for some time). There are many seeds planted for where the show can go in season 3, but we also got some significant closure. That is a rarity in TV nowadays.
Supernatural is easily one of the most underrated shows on television along with Friday Night Lights. If you are a fan of Buffy, Evil Dead, or just the sci-fi genre you really should give this show a chance on DVD. If you aren't hooked by the middle of season 1, then you probably don't like good TV.