Hero of Ages
the conclusion to the Mistborn trilogy.
The power Vin released was Ruin. It was a force opposed by Preservation. Preservation made humans with some ruin so as to get an edge on Ruin. Ruin was trying to destroy the world, period. Preservation gave up its sentience to imprison Ruin. Vin freed Ruin in Well of Ascension but joined the mists and took on Preservations power. Fought with, and joined with, Ruin. Sazed took both those powers and became The Hero of Ages, basically a god watching over the world. Vin is no more and Elend dies to, so no loose ends. The story ends with Sazed fixing the world and keeping it safe for the remnant of humanity saved by the Lord Ruler’s foresight.
Definitely didn’t take the direction I thought it would, but it was good none the less. Hope Sanderson does a good job on Memories of Light, the final Wheel of Time book.