I've been watching this show on and off for a couple years now, catching the odd episode when I can. A couple weeks ago, I decided to sit down and work my way through the first couple seasons.
I can officially say it; this show is AWESOME! It mixes superb acting with dark horror/action and some truly hilarious moments in a television vintage for the ages. Here's a description of the show stolen from cwtv.com, but it doesn't do it justice.
Twenty-three years ago, Sam Winchester (Jared Padalecki) and Dean Winchester (Jensen Ackles) lost their mother to a mysterious and demonic supernatural force. Subsequently, their father John (Jeffrey Dean Morgan, "Grey's Anatomy") raised them to be soldiers. He taught them about the paranormal evil that lives in the dark corners and on the back roads of America...and he taught them how to kill it.
For most of season one, I was just enjoying the cool action scenes and great special effects and wondering about hints at a plot twist, but I was completely blown away by the season finale. Somehow while I wasn't looking they sneaked a theme in there. The show had stopped being good and became great.
I should warn you, it can get a bit raunchy at times. Also, keep in mind it is firmly in the horror genre. However, and this is coming from someone who doesn't watch horror movies, the pure SCARY aspect of it was well within my threshold.
Now go watch it already!