This was sort of a fascinating episode of Supernatural, a show that is now older than God but still manages to spark with life from time to time. The show promised us another "metafictional" episode, along the lines of the Trickster and Carver Edlund romps or "The French Mistake," but delivered something very different.
In fact, last night's "Meta Fiction" seems to be a deliberate failure. Metatron tries to impersonate the Trickster — that wacky Mr. Mxyzptlk figure who turned out to be the Angel Gabriel in disguise — not only literally, but also figuratively. Metatron aims to screw with Castiel's perceptions in order to goad him into becoming the leader of the fight against Metatron, in much the same way that Gabriel tried to trap Sam and Dean into playing their roles in the prophecy, back in season five.
But Metatron is terrible at being the Trickster — absolutely wretched. It's not just that nobody follows his scripts, and the Winchesters foul up everything by capturing Metatron's minion Gadreel. It's also that Metatron is not that clever or inventive. His trickery is kind of obvious and clunky, and he doesn't have Gabriel's zing.
Also, Metatron's argument for Castiel is inherently flawed. As the Trickster, he argues that the Trickster and Castiel are unusual among angels, because they can think for themselves instead of just being drones. (But that doesn't necessarily make you a good leader. Often, a good leader thinks like the people he or she leads, and has been a good follower.) And yet, Metatron is trying to control Castiel — something that Castiel's independence of mind makes nearly impossible.
Until the end of the episode, of course, when Castiel finally does what Metatron wanted all along, and becomes the leader of the opposition, someone that Metatron can oppose and crush.
In any case, Metatron has clearly seen the assorted "meta" episodes the show has done before, and since his name even has "meta" in the title, he ought to be able to do one of those with ease. He makes a few mistakes, including too heavy-handed a narrator and the thing with Castiel's jacket — but chief among them is not making the Winchesters the main characters of his story. In this universe, "meta" only works when Sam and Dean are at the center of it, staring in disbelief.
In fact, the most telling moment of "Meta Fiction" comes towards the end — Metatron has implanted Castiel with knowledge of every book, movie, TV show and other media that the recording angel consumed over the past 2,000 years. So now, all of a sudden, Castiel gets a Star Wars reference that Sam and Dean make. And yet, he still doesn't get how it's a metaphor for storming Heaven. Because knowing all about Star Wars doesn't mean you understand Star Wars.
Also, Metatron wants to be God, which means he wants to be the ur-storyteller who created all these characters. But he didn't create them, and whatever he does, he'll be more like a fanfic writer than the author of Sam, Dean and Cas.
Oh, and there's finally some mention of fallout from Castiel stealing another angel's grace, a zillion episodes ago. Apparently it's burning out and it'll burn out Cas with it.
In the "B" plot, the boys have Gadreel prisoner, and Dean mostly does the interrogating while Sam goes to look for the missing Cas. Gadreel tries to get inside Dean's head by pushing all the buttons that are clearly labeled for anyone to see, and it nearly works — Dean nearly kills Gadreel, which is what he wants. There's a neat moment where you think that in spite of seeing through Gadreel's deception, Dean fell victim to the Mark of Cain and killed Gadreel anyway because of his compulsion. But then it's a fake-out — Gadreel is alive. Because Dean has free will, which means he doesn't need to follow anybody else's storyline. He can make his own damn mistakes.