I find street photography to be a deceptively difficult area of picture making, and I mean in both excution and definition, as well as criteria for judging it. It is a subjective thing in many ways - but lets not use that as an easy way out (no here has, so far).
It (street shooting) is dotted with traps and pitfalls - from actual, present danger to ones person, through those threatening the artistic integrity. The line between documentation and exploitation. The often seen lack of that all important compassion. Hell, the pictures that are not meant to be compassionate - is a condemning image a bad street photo? There are things out there, everywhere, deserving nothing but contempt, too!
On the other hand, I have seen so many takes on street photography, so far ranging in their unique apporach, that I believe the lack of exploitation and ability to contain meaning into the image which is technically competent are the only two absolute must-have's.