I think it is important to remember that nobody including John Williams has ever matched John Williams from 1975-1984. Every single score he did was brilliant-even for throwaway movies like Dracula and Jaws 2. That was his creative peak and all 3 of the original SW movies fit into that time period.
That said, I did think Ep. I was excellent. Think of Duel of the Fates, The Flag Parade, Anakin's theme. It was a very good score. I think not nearly as much effort went into Ep. 2 and 3, but can we blame him?
I thought "War Horse" had some welcome energy in it- I wholeheartedly believe that if JW is presented with an outstanding movie, he will rise to the occasion.