Supernatural is one of the best series I've ever watched. The serie is about the story of two brothers "Sam" and "Dean" which are hunters. But, they don't hunt animals, they hunt creatures such as ghosts, vampires, demons, etc.
In my opinion, the best period of the serie is from season 2 to season 4. The first season is only an introduction of the characters and creatures. At that point, they cross the country pursuing clues of their father who is disappeared. And, from season 5 on the story just get boring.