If the task was impossible for one man, however, why not two? Christopher Tolkien's great achievement has been to be that second man, and to place his father's work into a coherent, over-arching context. Among his chief triumphs, from a literary rather than a critical perspective, have been presenting us with The Silmarillion, The Lays of Beleriand, and The Children of Hurin (not to mention such non-Middle Earth related gems as Sir Gawain and the Green Knight and The Legend of Sigurd and Gudrun). The question, then, when reading The Unfinished Tales is how they fit into the greater context created by Christopher Tolkien for his father's post-humus works.
Following Shippey in his Road to Middle Earth, I'd like to suggest that The Unfinished Tales ought not to be read as "authoritative" answers to various problems and overlooked details in The Hobbit, The Lord of the Rings, and The Silmarillion, but rather as Tolkien's tentative, unfinished attempts at harmonizing and expanding the vast body of literature he had created. Christopher himself points us in this direction with his sections of critical commentary offering variant stories and explaining where his father seemed to be toying with abandoning one explanation or another (see the Nazgul's fear of water in The Hunt for the Ring). This view of the book, however, makes it a bit unsatisfying if the reader is looking for "more Hobbit, Lord of the Rings, and Silmarillion. Readers of The Unfinished Tales need to adjust their expectations and instead view the work, as it seems to have been intended, as an insight into Tolkien's ongoing creative process; not a set of definitive answers.