Having just finished producing a staging of Mitchell's translation of the Book of Job, I can vouch for his superior translation of the intensity, color, and tempo of the book. His words are strong (sometimes stronger than the Hebrew), and his consistent three-beat-per-stress treatment lends audible poetic unity to a book that, in many translations, can seem a verbal mush. His essay isuseful for its esoteric parallels, and is enjoyable reading. Like the translation, though, the essay explains by simpliying the book.
This simplification is built of numerous omissions,reversals, rewordings, rearrangements, insertions. Often the poetry is simply his, not the text's. As Mitchell will occasionally note in his comments, he "improvised radically." Indeed.
So, use the Mitchell to lend color and tempo to your reading of a more accurate translation. (The new Jewish Publishing Society translation is excellent) Use Moshe Greenberg's essays, perhaps, to provide a sense of the complexity and depth of the book. If read alongside a more accurate translation, the Mitchell will prevent it from being dry -- no small thing. Let Mitchell help your hear the book, let another translation help you see it.