C. Tolkien books worth reading?

Christopher Tolkien’s role was that of an editor, not a ‘finish it’ author.

The Children of Húrin is a novel, as that was the story that was most finished by J.R.R. Tolkien, and Christopher had enough material from various versions/drafts to edit together a complete narrative.

Unfinished Tales is the next most like a book of stories, though not all the parts of it are, and it does have commentary (though not large sections of poetry). The Túrin part of UT was used for the Children of Húrin, but aside from that the Tuor section, Aldarion and Erendis, and the Third Age materials are very much narratives, even if incomplete.

After that you are down among the weeds of the editorial analysis of drafts in HoMe and the synthesis of Beren and Lúthien, and the Fall of Gondolin.

Other have mentions 'children of Hurin' and 'Unfinished Tales'. The history of Middle-Earth series also include volumes like 'sauron defeated' that contain stories/texts from the Legendarium. My particular favourite legendarium text is in fact 'the Notion Club Papers' from 'sauron defeated'. The text runs for over 100 pages and is really an abandoned novel. If you expect the lord of the rings or the hobbit you will be disappointed though as this is something quite different. 'The lost Road' from 'The Lost Road and Other Writings' is an abandoned time-travel story and is also a favorite of mine among the legendarium texts.

For anyone new to the HoMe series, I'd also particularly recommend the volumes that relate to the writing of LOTR (6 to 9). Even if you don't think you'd necessarily find the years-long development of the story interesting, give it a try. There's a wealth of fascinating detail. Some elements are relatively well-known (e.g. Strider was, in an earlier iteration, a Hobbit called Trotter), some not so much. One thing that stuck for me is the abandoned idea that Gandalf would confront several of the Nazgûl when they attack Crickhollow. There's only a short piece of narrative but it's quite exciting!