So I have completed the new Sanderson "extra" book, The Fires of December. It is part of the collection of side stories that started with Tress of the Emerald Sea that flesh out the Cosmere and add many little teasers to the setting.
I did enjoy it very much, which is the short review. While all characters besides the main characters do feel a bit flat, I am as always resonating well with Sanderson's style.
From what I read on general opinions about the book, it is as polarising as modern Sanderson books tend to be - not everybody likes his writing, worldbuilding, and humour. But the most controversial part has been a relationship occuring in the book, which I won't spoil, but does appear problematic on first glance with contemporary ethics. But to me, in a fantasy setting it is more of opening a question to discuss. I personally do not find its portrayal questionable, but it is not the first time that a "real ethics" discussion bleeds into a fantasy novel and creates more breaks in suspension of disbelief than a dragon lifting itself into the air.
If you are invested into the Cosmere, then you should consider reading it, if you have never touched Sanderson, it will be more confusing than anything else. Go try Mistborn instead if I made you curious.
It is also roughly his 40th publication since GRRMs "A Dance With Dragons", which shows that some people just cannot stop writing if you like it or not.