Yeah, the books are formulaic, but it's a good formula. "Act 1: Okay, here's a neat magic system with well defined rules. Act 4: surprise, there was an extra rule you didn't know about! Act 5: we killed God with the surprise, extra rule."

It's hard for me to fault Mistborn. It has the tightest ending to a fantasy trilogy I've ever seen. And then, as an afterthought, Sanderson somehow managed to end the Wheel of Time, which frankly I don't think Robert Jordan could have managed to do.