Defense Secretary Robert Gates has been giving valedictory speeches and press interviews as his June 30 retirement approaches. As someone who has studied the various Pentagon leaders, I have nothing but praise for Gates in all of his challenging roles -- manager of the Pentagon, presidential adviser, diplomat, and war planner and war fighter. Leon Panetta may turn out to be an excellent SecDef, but he'll certainly be different from Gates and it's unlikely he'll be as effective.
Gates has been mild-mannered (at least in public) but tough -- especially in firing several senior officials for poor performance of their duties. He also imposed a near-term focus on an institution that historically cares mainly about preparing for future wars.
Among the best recent articles are ones by Fred Kaplan at Slate and Mike Allen in Politico. When more good retrospectives are written, I'll send them along.