Of late most of the critics are using the words 'subtle performance' to praise the performance of an actor. According to them, 'subtle' means the performance of an actor that has no overrated dialogues and no overrated expressions in face and body language of an artist.
However, some of the critics are coming up with a contrasting definition for the word 'subtle'. They feel that some of the actors can't express all nine elements (navarasaalu) of acting. Whatever the role do they play, they usually exhibit just one or two expressions through their faces in films. Obviously, their performances are treated as 'subtle' performances.
Whatever it is, a sensible and talented artist should be ready to do any kind of performance related to all nine elements of acting. Then only, he can be called a full-fledged artist. Else, he remains to be a subtle performer.