Professional and weekend artists have many differing opinions on the viability of art critiques as a way to improve ones artistic ability.
Some say they are useless, because that would assume there is a list of common rules that a work of art should follow in order to be considered correct. Due to the fact that art is a freedom of expression it is not bound by such earthly constraints, so how can it be critiqued if it follows no rules.
Artists on the other side of the issue feel that art is nothing but a set of rules and techniques that take a lifetime to master. As a result art critiques are as simple as spotting the artists flaw in technique and correcting it. They believe by repeating this process many many times an artist improves, and eventually becomes a master of their craft.
I feel the viability of art critiques is a mix of these two paths of thought. First off art is a freedom of expression and is not bound completely by such earthly constraints. Although there are a few fundamentals such as perspective and lighting which make artworks look more realistic, they are not vital to the process.
These fundamentals are one (albeit a small) aspect that can be used incorrectly, and easily critiqued by others. At the same time there are other aspects such as style and personal preferences which greatly affect the resulting work, but are specific to the individual and are never incorrect, thus it is ny impossible to critique.
Considering all this I believe art critiques can be useful to some degree. You must remember to take any critique with an open mind, think about what is said and look at it as a neutral observer, do not get to emotionally involved. It may just be that your art is different than most mainstream art, but you work will never evolve if you do not get other artists perspectives of it. As we all know personal bias can sometimes stop us from seeing what is right in front of us, and an artists artwork is no different.