Graves’s translation of <i>The Twelve Caesars</i> was a formative work in my teenage years and (along with <i>Das Glasperlenspiel</i>) defined my view of humanity for some considerable time and still rings true many decades hence.
His "Goodbye to All That" is a good memoir of the First World War. Though his Mythologies are the most readable or engaging one. I prefer Thomas Bullfinch for Mythology.