I think that constructive criticism should be the cornerstone of this forum especially for us beginners,otherwise what is the point when every comments on work is the same( is beautiful,great...).One thing is the artistic aspect of the work(concept,idea..)and another thing the technical part(using photoshop tools,blending pictures in bacground,colors,choosing the right stock picture....)
For example in my manipulation for speace challenge(Brave Explorer)I showed my work to my friend(more experienced Photosop user)and he pointed out technical flaws in the work(colors ,exposure,shadows,blending of rover in bacgraund)and I corrected them,without his criticism I would have believed that the work is good(Technically speaking).
I believe that learning photoshop is very similar to learning traditional arts you must first master the basic techniques(portraits drawing, oil painting techniques,watercolors......)before you can create your own works of art.