He plays as if there is a wasp in the concert hall and he is keeping a close eye on it.
That, hands down - no question, is the best description/explanation I've read on his behavior at the piano.
My own experiences - heard him play Prokofiev 3 before he hit it really big, I really enjoyed it. Two years later I heard him play one of the Chopin concertos - it was a nightmare, I got the impression that he really didn't understand the music.
(BTW, I close my eyes to listen at every concert - so I really didn't know about Lang Lang's histrionics until you tube!).