I love a lot of season one, but there is something to be said for the actors knowing their characters more deeply and having the ability to convey that to the audience [in Season 4].
It had a dark intensity to it that was injected with humor here and there. There was a subtle sense of energy. The eerie stillness of no background theme or sounds in most scenes really lent itself to keeping me riveted.
Supernatural has carved out a nice little niche for itself, and even though I'm not a particular fan of horror-related fare, I think the show executes what it sets out to do with quiet efficiency and well-earned confidence.