This talks quite a lot about the perception of the listener, but what about the player? The responsiveness of an instrument is one of those remarkable attribute

This talks quite a lot about the perception of the listener, but what about the player? The responsiveness of an instrument is one of those remarkable attributes that isn't often perceptible or appreciated by the audience -- the willingness of the instrument to respond to player input, which is part of the expressiveness. A performer can compensate for a "dull" instrument to a degree by anticipating a note and/or playing with greater force, but this has its limits. It is very subjective, and I would think difficult to measure, but some instruments are truly magical and feel eager to perform. It can whisper or shout, or ring on certain phrases, or more easily leap wide note intervals without unattractive overtones. Others, ostensibly identical (even made with wood from the same tree), are lacking something and aren't as responsive.