Mistborn: Secret History has so much information in it, it is astounding. 
 While also being a novella on its own, it's a behind the scenes for several of the major events in the original trilogy, gives us some more insights in the Cosmere, Shards, Realms, and Adonalsium, and it brought me a bit of much appreciated closure. 
 Two days after finishing this I am still struggling to digest all of its implications, and while it answered a lot of my questions, it also raised several new ones for me, or might have simply made me more aware of questions I already had. 
 (view spoiler)[1. What exactly is the devise the Elantrians had? 
 2. What is Hoid's alignment? I thought he was kind of cruel in Mistborn: Secret History. 
 Then I re read the whole Hoid-Kelsier scene and realized that he only hurt Kelsier after Kelsier threatened to murder him in a cruel way (slice the tendons on his wrists, slowly crush the life out of him, remove his fingers one by one etc.). All that and more left me a bit puzzled concerning Hoid's real nature / intentions in the Cosmere. 
 3. What has happened to Marsh? Is he the man with "Iron spikes for eyes", referred to in the Alloy of Law and mentioned in its epilogue as a man Marasi has to confront and who she thinks is "Ironeyes"? 
 4. How was Spook instrumental in bringing together the new empire after "The Hero of Ages"? 
 5. How exactly were the Bands of Mourning created? 
 I hope to find answers to some of these questions in "The lost metal". (hide spoiler)] 
 Some thoughts about the characters and events of Mistborn: Secret History, 
 (view spoiler)[so after Kelsier (sort of) died, he went to the cognitive real, punched God in the face, recruited him for his team and gave him the nickname, "Fuzz". 
 Oh, I missed you so much, Kelsier. 
 I loved the conversations between Nazh, Khriss and Kelsier, for they gave some real insights in the Cosmere. The following one was one of my favorite conversations in the whole book: 
 "So . . . my world, and everyone I know," Kelsier said, "is the creation of a pair of . . . half gods?" 
 "More like fractional gods," Nazh said. "And ones with no particular qualifications for deityhood, other than being conniving enough to murder the guy who had the job before." 
 "Oh, hell . . ." Kelsier breathed. "No wonder we're all so bloody messed up." 
 "Actually," Khriss noted, "people are generally like that, no matter who made them. If it's any consolation, Adonalsium originally created the first humans, therefore your gods had a pattern to use." "So we're copies of a flawed original," Kelsier said. "Not terribly comforting." 
 He looked upward. "And that thing? It used to be human?" 
 "The power . . . distorts," Khriss said. "There's a person in that somewhere, directing it. Or perhaps just riding it at this point." 
 Finally we got to meet Vin and Elend again, if only for a brief moment, but we had a proper good-bye this time and it was comforting to witness that both seemed content to go beyond the Realm together. 
 (hide spoiler)] 
 If you are interested in the bigger picture and like to pay attention to all the Cosmere stuff in Sanderson's books, this one is a must read. 
 Highly recommended.