How much of Children of Hurin did Tolkien actually write? I'm reading the Silmarillion right now and am thinking about reading it next but I don't really want to read something where they just took a basic outline of Tolkien and wrote a book around it. I get the feeling that the Silmarillion was more or less almost all his writing and Christopher just pulled it all together? Is Hurin similar or did they just to something like take the Turin chapter from Silmarillion and expand on it?
It's almost all genuine JRRT stuff. Most of it had already been published in Unfinished Tales, so if you've read that book you won't me getting anything new in the 2007 version of
The Children of Hurin, other than a more polished product. Anyway, the 1977 version of
The Silmarillion is by no means "more or less almost all" of Tolkien's writings on the First Age. Tolkien went through and wrote numerous different versions of the First Age material, including multiple novella-length (or longer) versions of the major tales, several different (highly detailed) annals, thousands of lines of narrative poetry, and extensive essays on background stuff. The version that was published as "The Silmarillion" is a selection of material written over the course of some 50 years, with the inconsistencies ironed out by the editorial actions of Christopher Tolkien. It actually has far
more new, Christopher-written material than any of the other posthumous publications, because Christopher changed his approach to editing his father's works afterwards, and was less concerned about presenting something internally consistent and more about showing the evolution of the works over time.
I just finished it. It does feel very genuine and the Silmarillion version was VERY much abridged from existing material. Tolkien himself wrote a huge poem version which probably was the base for the novel.
It's also not very long so there's that.
There was a poem version,
The Lay of the Children of Hurin, but the novel is a polished version of Tolkien's prose story,
Narn i Hin Hurin, which was written after the poem. (Both versions were preceded by the original Book of Lost Tales-era
Turambar and the Foaloke, but that has all sorts of weirdness as Tolkien was still in his "mythology for England" phase and most of the recognizable elements of the legendarium had yet to be hammered out.) Tolkien also attempted a new prose version of the story of Tuor, taking into account all that had changed since BoLT, but unlike the Turin story, Tuor's never progressed past the introductory stuff. What does exist of it, breaking off with Tuor about to enter the city of Gondolin, was published in
Unfinished Tales.
You're correct that the version of Turin's story found in the 1977
Silmarillion is the abridged version, rather than being the basis for the longer version. This is true of pretty much the whole book, though unfortunately, only Turin's story has a complete prose version written later than the 1910s.