This is absolutely one of my favorite shows, and easily my favorite episode of season 6. The season 5 finale, Swan Song, was just so well done that it's been hard to get into season 6. The first half of the first Kripke-less season has seemed very aimless with trying to save Sam's soul, bouncing back and forth between the Winchester's connection to their mother's side of hunters, that the throwback to S5's Apocalypse just felt comfortable.
The in-jokes in this episode made it fun - way more fun than S4's The Monster At the End of This Book, and I only hope this episode begins a story arc as good as that episode did. In the arc of the series, it's not the greatest at advancing anything, but it was a great wink and nod for the show's fans. A total tongue-in-cheek episode highlighted by the Youtube clip of Jensen Ackles from Days of Our Lives [with a better storyline than anything Days is running now, but I digress]. I'm not sure we'll get a season 7, so this episode made this season for me. :)
Sorry, but to drop another Simpsons line, now that didn't make a lick of sense. Homer's reply is actually "There's an Air In Space Museum." Man, I thought this line was from when he was on the space shuttle in Deep Space Homer. D'oh.