As a finale to Season Eleven, this episode kind of sucked. As a jumping-off point for Season Twelve, with a solid wiping of the slate and some new elements thrown in, it was quite good. So... I'm torn.
It's hard to describe exactly what was so unsatisfactory about the bulk of this episode to me. Individually, I thought a lot of the moments worked really well, but when they coalesced, the final product felt thin. I knew that the stakes were high, what with the sun dying due to Amara and Chuck being "out of balance," but even with God on the verge of death and Dean preparing to sacrifice himself, the whole thing was pretty easy to shrug off. There wasn't much of an emotional journey for Dean and Sam to take here, since we all know that they will be back for Season Twelve. It makes the tension a little hard to maintain. To compensate for that, they focused on God and Amara's emotional arcs. Which is fine... but a bit odd for a season finale.
The resolution of our main plot was pretty anticlimactic. Think about all the buildup we had. Amara wanted to turn the world into nothingness. She had this weird creepy connection with Dean. In this episode, Dean and Sam collect souls from ghosts, and Billie lends an assist by getting souls from the veil. Rowena puts all these souls into Dean, and all he has to do is get close to Amara and set off the Soul Bomb, and Amara will be killed. Only... instead of doing that, Dean gives Amara a talk about the importance of family. Amara brings Chuck to her, and heals him. The two are reunited as siblings, and they decide to go away for a while, but not before Chuck removes the souls from Dean and saves him.