4/5 - I read this in Arcanum Unbounded* - it has a million spoilers for Mistborn. Do NOT read Secret History first. I'm happy I now know what went on "behind the scenes" during the original trilogy and I thought this tied everything together neatly. It wasn't perfect though, it did feel a bit disjointed at times and a couple of the connections felt forced. Still a great Sanderson read. 
 This was me the whole time I was reading: 
 *I'm currently only reading the three Mistborn stories. I'll save the rest of this book for when I finish Sanderson's other series.