Certainly the best SoS potentially since Robertson 25 years ago. On top of his brief, prepared to admit past failures and not afraid to ask for more funds and to take hard decisions. While there's still lots to fix, you don't undo decades of overstretch and neglect in a couple of years. Compare and contrast with some of his predecessors.....
Buffhoon, Reid, Swiss Toni - the job-share SoS, Ainsworth, Fox, Fallon, Williamson.
I've omitted Hutton and Mordaunt on the basis they were both here today, gone tomorrow and Hammond was essentially brought in to make the hard decisions in SDSR2010. Once those were made he shifted aim to his real ambition.
ETA : Heappey might be the best shot for a replacement. He too "gets" defence, as did Alex Chalke.