The dictionary meaning of the word 'subtle' is 'so delicate or precise as to be difficult to analyse or describe'. However, as per cine analysts' language, 'subtle' means a decent/natural performance without overrated action.
In the recent past a few big stars have been lauded by the analysts as the actors with subtle performances. Since they received the same appreciation for every film, a few big stars have connected to those praises.
Eventually, aforesaid big stars started exhibiting the same performance in every film. Moreover, they are exhibiting a little expressions in their faces and have felt it's a performance with international standards.
Sadly, the same actors are now being criticized for expressionless acting. It doesn't mean that they would be advised to perform like 1950s and 60s heroes, who resorted to do over action in their films. The big stars just need balanced performances with balanced expressions and body language in their films that suit to their roles. Obviously, they can follow the footsteps of legendary performers like Megastar Chiranjeevi in industry to get their mistakes rectified.