Perfect blend of supernatural elements/alternate reality/humor/action & drama
However, half way into the season, the guys started to own their characters and the writers started to have some fun too.
It's really the awesome pop culture references/jokes that I love the most. Sometimes they are really subtle and you gotta be quick to catch them. Sometimes they are so blatant and crude they make me gasp then crack up till I hurt.
The best thing about Supernatural is that it's not losing steam as years go by - each season seems better then the last.
The writers are really the heroes of this show - though it doesn't hurt that there's some serious man-candy available for my viewing pleasure too...
Love, love, love the unapologetic lack of political correctness!