I think it's possible for someone who has a lot of knowledge of a certain field of art or music to give truly constructive criticism, in the sense that they might not even like the genre or style of a piece, but they can still see how it should work to be as good as it can be within this genre. A big part of quality is of course "personal taste", but it can also having a clear vision as opposed to being obviously not sure about what you really wanna say, sticking consistently to your vision instead of half-assing it; how a work is presented. Quality can be the exact point where you draw the line between "too minimalistic, something is missing" and "this is too much", etc. These are of course subjective at the end of the day too, but they can be argued and discussed as opposed to simply "this is good" or "this sucks".
All artists know that showing your work to someone else can turn everything on its head; the points that you thought were obvious are lost on someone, who instead picks up on other things not even intended, the work you think is the weakest is the one that gets the most praise, etc. Going to other people for criticism (a label owner, an art professor, your mum..) doesn't mean you have to change everything in accordance to what they say, but you will have to consider it. Why does this person have a different view of your work than yourself and does anything need changing, and if not, you should be confident enough to stick by your original idea anyway.
One thing that strikes me while reading this thread, though... a lot of you say that a work should be evaluated against the rest of the artist's catalogue, does it stand out or is it just average, can they do better, etc. This clearly can't be applied to debutante artists, so in that case there should be a higher degree of subjectivity involved perhaps?
