In one word, phenomenal.
My favourite episodes are always the odd ones: "Weekend a Bobby's (6x04)", "The Man Who Would Be King (6x20)", "The French Mistake (6x15)", "Fan Fiction (10x05)", "Monster Movie (4x05)" or "Bitten (8x04)".
But this episode... this episode IS the very essence of "Supernatural", it IS the show. The call-back to "Swan Song (5x22)" is very cool and everything else about this episode is just perfect: it hits the perfect note in every scene, on every dialogue.
This kind of episodes are why people love TV shows, and why there are fandoms. The writers have done a beautiful job and I think this episode has just become my favourite 40mins on television.
Fans can love this episode and the writers and actors for it, and newcomers can watch an impressively well executed piece of drama that'll hook anyone for 11 seasons (and counting).
The Impala hadn't received a proper episode yet, now justice has been done.
Welcome home, Baby.