It started when I was working my way through the first two seasons on DVD - I would watch an episode, love it, and then check the writer and director. There seemed to be a pattern. :) I especially loved episodes written by Sera Gamble & Raelle Tucker, as well as episodes directed by (the one and only) Kim Manners. So now I pay attention to that sort of thing. And Production Design, and Executive Producers... I dunno, sometimes a show is only as good as it's crew. And SPN has and amazing crew - which is why it's so noticeable when newbies come in to write or direct.

I heard that there actually was a manual. They have to keep the show's mythology straight and the general plot arc so a writer doesn't come in and create a massive plot hole. But with this show, you really have to know what's going on and understand the characters. Otherwise you get episodes like this.