Our personal recommendation from experience is the Bradt Guide. It is factual, accurate, clear and has a no nonsense approach, informing you in detail about the good, the fantastic, the amazing, the irritating and the down-right ugly!
Geographically Ethiopia is stunning. The landscape is dominated by the dramatic Ethiopian Highlands with peaks of 4000m or higher. The country is bisected by the Rift Valley, which starts at the Red Sea, to the North East, and continues south to Mozambique in southern Africa.