It's one of his unpublished works, which you can get by mailing him.
It has the wells you find in Mistborn, along with the same secret those wells hold. It is a story of two gods clashing, and men caught between. As in all Sanderson's works, it comes with a really cool magic system, this one about special abilities that can be "grown". Some can grow vines to fight with, some can grow rocks to make armor and blades, etc.
I love love love Brandon Sanderson. Sometimes I find him guilty of being a bit "gee golly" with his characters, especially the male leads who end up overcoming adversity and becoming pure-hearted leaders (Raoden, Kaladin). Aside from that, I find his writing very enjoyable and I always fall in love with his characters. I also appreciate that his stories contain a lot less sexual violence than a lot of mainstream fantasy.
Brandon Sanderson is amazing. As my heterosexual male best friend so classily put it after reading his books: 'I want his babies'. I think my favourite was 'The Well of Ascension' but it's so hard to choose. Anyone else have a soft spot for TenSoon? Also, you say you've read his unpublished works? Can anyone ask for them? I'd really like to read them if possible.
Rebel Commander - Leading the resistance against Evil Overlord Stephan van Velzen