The idea of criticism is surely a slippery slope both for the artist who seeks it and critic or adviser giving it. One point I have to agree with is one needs to see a body of work rather than a single work to give a fair assesment of an artist. No one piece defines an artist especially throughout his or her lifetime. Artists evolve over years as they grow and find new subjects to comment on. Finding a critic that would be beneficial to you is harder than finding a doctor. Critics can rarely be subjective when looking at a multitude of artwork from various artists at any one time. 
So the ongoing dilemma is who does an artist turn to for advice? The one and only answer, meager as it sounds, is the artist themselves. You have to be your own critic.
This is scary stuff especially when you are learning and unsure if any progress is taking place with your artwork. But only YOU know what it is you want to say, what you want to accomplish.  No?
Then maybe the first question an artist should ask him or herself, is why do I want to paint this subject?
If the answer comes back “because I like it or is fulfills me or I enjoy it, fine. Then don’t look to critics at all.
If the answer comes back that you have a burning desire to change the world or make a statement on your time or life or you can’t stop thinking art or the burning in your gut won’t subside until you sit at your easel, then you should think about seeking counsel.
Look to other artists’ work, find comradery in other artists, then look into yourself. You will certainly reach a point when you know you are on the right track no matter what anyone else may think or say. This will take time. As your ability grows so to your confidence, also your ability for self counsel.