I wrote pretty much this in my (unposted as of now) review. In my head, this would have made a perfect series ending (with both Sam and Dean in the pit). I've never believed that they would have a "happy ending", but always thought that they would die side-by-side for some heroic cause. This could've been that moment, except the knowledge of a sixth season sort of made all of that anticlimactic for me.

As for Chuck, I think that was just Kripke being cheeky about the writer as God. Isn't every writer God to his/her own creations? :) I actually quite liked that last narration about the difficulty of writing endings, which is another reason I'm disappointed this wasn't the series finale, because everything was set up perfectly for it to be the end.