That look on Sam's face, determination and desperation mingled in his eyes and the stubborn set of his jaw, while Dean looks away in stoic acceptance of his fate, is absolutely heartbreaking when we know how it ends. And because I had read all of the episode summaries ahead of time, I knew how it ended. I don't know--did people watching it live know from spoilers that Dean was going to Hell? I can't imagine how shocking it must have been when the good guys couldn't pull it out in the end. By the time I got all caught up with the first three seasons, S4 was only a week away. How hard it must have been to wait all through that summer!
Funny story: the second SPN episode I saw after "Skin," because this was what the CW website's free episodes were showing at the time I started watching, was "Red Sky at Morning." Universally acclaimed as one of the worst episodes ever, but it got me hooked. Maybe because of the lampshade they threw on Dean-in-a-tux, maybe because the MOTW was about brothers, IDK. Maybe because I went back and started at the beginning of the season, where "The Magnificent Seven" and "The Kids Are Alright" were so good, and then BDABR, which remains one of my top ten eps for "I lost my shoe," if nothing else. "A Very Supernatural Christmas" was perfect from start to finish. That's one I need to watch again someday. "Jus in Bello" was the next of Sam's tough choices that he didn't make, sparing Nancy's life when she was doomed anyway. How things would have been different if Lilith had been stopped then! And oh, if the writers' strike hadn't happened and Sam had gone dark side to save Dean. *shakes head for what is and what will never be*
For the same reason I've only watched AHBL once, I've only watched "Mystery Spot" once. I just can't bear it. And I won't even tell you how many years it took for me to be able to listen to that damn Bon Jovi song again.