Definitions of discerning:

• adjective:   unobtrusively perceptive and sympathetic

  Example: "A discerning editor"

• adjective:   having or revealing keen insight and good judgment

  Example: "A discerning critic"

• adjective:   able to make or detect effects of great subtlety; sensitive

  Example: "Discerning taste"

• adjective:   quick to understand