I think the finale was a bit indicative of the season as a whole. It seems as though the show writers are not nearly as imaginative as they used to be [and are running out of new, exciting ideas]. The biggest problem, in my opinion, is that the writers aren't following established rules of the Supernatural universe. It's one thing to have a well explained revelation which causes characters to question previously established lore, it's quite another to have stuff just happen that directly contradicts previously established rules, that drastically affects the storyline, and that gives no explanation as to why it's happened differently this time.

Exhibit A [and the biggest issue I had with the finale]: Why did Dean say 'yes' and why the fight between Lucifer and Michael take all of 2 minutes and not cause any damage whatsoever? We spent entire seasons of this show watching Dean fight against possession by Michael; he was tortured, he watched Sam being tortured, he was sent to the future to see what would happen if he said no, he helped Sam lock Michael in the cage with Lucifer [which started the entire civil war in heaven]. 'Team Free Will' took every other avenue they could think of to prevent Dean from saying 'yes' and to prevent the damage [destroying half of the planet] that would be caused by Michael and Lucifer fighting.

So why the flippety fuck did Dean spend all of ten seconds deciding to say 'yes' to the one person/angel he should trust the least out of anyone in both universes, and then gain his impressive, world destroying levels of power, to just float around a bit before killing Lucifer with the friggen archangel blade? What was the point of becoming Michael in the first place? Aside from the terribly convenient arch angel blade being a thing in the first place [which has lore contradicting issues in itself] Dean has enough experience dealing with Lucifer at this point, he could've come up with a plan that did not involve handing Michael, the guy who has been their No.1 enemy for the entire season [and was finally weak enough to be killed/captured/removed from the picture], the one thing he needed at that moment to be able to destroy the world.........