Each area of art requires its own set of criteria when determining good and bad, i.e. painting, sculpture, print-making, craft, conceptual etc. Personally I hold originality to be important in this determination. For contemporary artists that can be tough. Most of what is being created today is, in my personal opinion, not very original. To me a Mark Rothko is a masterpiece, while a thousand color-field artists after him are not. I find Pop artists brilliant and Jeff Koons completely reactionary. There is originality in contemporary art, but it is tough to find.
It is also tough when the art market influences good and bad. I would like to say that monetary value determines quality, but unfortunately they are often unrelated, as many factors can influence the value of artwork other than quality. Damien Hirst is an interesting and relatively unique artist, but I don't think his prices at auction reflect how good he is. When one of his works is worth more than a good Monet landscape, something is very amiss.
that is what they are saying