I have to say I am perplexed by peoples desire to see musicians smiling in a concert..the level of concentration required demands total focus which is probably why most of the time they aren't smiling and look serious about what they are doing, after all the audience is paying good money to hear a concert or recital, they are hoping for the performers best and that takes a serious level of concentration. Sure they all smile like crazy in an Andre Rieu concert, it is a much lighter hearted affair, but I suspect the Berlin Philharmonics audience is hoping for the pinnacle of performance and execution and couldn't care a tinkers cuss if the Orchestra is smiling or not, they paid big money for those tickets and expect something for their return.
Also I have no problem with an artist who gets emotionally involved with their performance, it shows a connection with that which they have poured their heart body and soul into, some works take years to bring to concert level and the artist is naturally connected on a very deep level to what they are playing..I am not so self conscious that someones performance is marred because they demonstrate a physical reaction as part of their performance. I doubt the performer even realises that they are doing it..Music, like all arts are by their very nature physical and the performer can either show delight, sadness, intensity or joy in what they are communicating, it is no different to the physical actions we all use day to day in conversation, it is part of how we express ourselves..why would a performer be any different, why would it not be magnified as they try to communicate with an audience, sometimes of many thousands..
Before we critique a performer for performing, I suggest that maybe we should perform at that level and see what it's like.