WordNet sense 1 (having or demonstrating ability to recognize or draw fine distinctions):

acute, incisive, keen, penetrating, penetrative, piercing, sharp, knifelike

WordNet sense 2 (having the ability to perceive or understand; keen in discernment):

perceptive

WordNet sense 3 (tending to select; characterized by careful choice):

selective

WordNet sense 4 (selecting what seems best of various styles or ideas):

eclectic

WordNet sense 5 (noting distinctions with nicety):

discriminate, nice

WordNet sense 6 (able to make or detect effects of great subtlety; sensitive):

discerning