We all love this one for the wonderful growing relationship between Dean and Cas, and wail at the horror of everything Sam experiences-- from being force-fed demon blood, the compounding guilt, the fear that he can never get out or his life and destiny can never change, and his first face to face with Lucifer... it’s a big one.
How free are they, really? Is destiny still coming for them? Are they doomed to play out the Grand Narrative being written for them?
(points forcefully at the series finale and screams incoherently)
Links that may be of interest:
The Superwiki page for this episode
My rewatch notes from June 2019
The CW promo video for this episode
Lizbob’s two posts from the Dean and Cas are in love series (here and here)