My main complaint about this season has been the lack of any sense of grandness to the Apocalypse. While that argument still holds water, "Swan Song" fully crystallized the reasons why Eric Kripke and his team went down the path and in execution and boldness, their ultimate goal ended in wild success, hitting the right notes from beginning to end.
Although the big names--God, Lucifer, Michael, angels, demons, Apocalypse--were thrown out there, the heart of the show will always be and remain the enduring relationship between Sam and Dean. The outside world and even Cas and Bobby can be seen as external factors, not very important as far as the show is concerned.
The episode is framed around Chuck writing his final story, the story about the Impala, the object symbolizing Sam and Dean. Chuck doesn't write about how the world is about to end or the major implications. It's all about Sam and Dean. In the eternal struggle between good and evil, there's little Sam and Dean could do. I'm sure many people died in the earthquakes, but we never really see the consequences save for a few moments on small television screens.
And that's what the show boils down to. Supernatural was never a big picture show, whirling around with big ideas and statements, and big picture names in the final stretch of a 5-season arc never changed the internal makeup of the show. It started as two brothers fighting things that go bump in the night and ended as two brothers who fight things written in pages of the Bible. Through it all, Supernatural stayed true to its origins.
The one thing I was looking forward that I didn't get was a fight between Lucifer and Michael. It was hyped from the beginning, and something more than a little pulling before going through the portal would have been nice. Still, the lack of fighting between Lucifer and Michael plays back into the connection between Sam and Dean. Dean directly confronts Lucifer, in his brother's body, and it's the Impala that saves everyone.
Looking ahead, Supernatural was renewed for a sixth season though Eric Kripke won't be the showrunner. There's still some things to be resolved. Sam pops up at the end of the episode and Sam has to be part of the show in later seasons. I kind of want to know more about Heaven, although there were major implications that Chuck is God which didn't make much sense.
Score: 9.7/10