Sure you can judge. For starters, da Vinci never finished it! :-)

"Good art" is a judgement call so that it's different for everyone. Until the artists put values on the definition of "good", we'll never all agree. And that's why the janitor's still a janitor (although if he thinks that "good art" is absolute and he has the final judgement on it, maybe there's a career for him in teaching...)

Graham.