His forehand, his biggest weapon, is just not anywhere near as good as it use to be - that's the biggest difference to me.
There have been times this year when he's looked tired in matches. He doesn't seem to have as much fight as he use to have. I think he's also a couple of steps slower than he use to be.
I don't think he's changed his style much. He does still struggle against the big servers. This year, he's had problems with a variety of players. J Johansson, Roddick, Behrend, Mirnyi, Ljubicic and Berdych are all big servers who have beaten him. While Coria, Nadal, Davydenko, Ferrer and Clement are all grinders who have beaten him.
But it does seem strange that he's done better at Wimbledon than Roland Garros for two years in a row now.