It depends, of course, who's looking.
Most graffiti is an urgent, even aggressive, expression of an urban subculture.
Conformity isn't usually one of the preconditions for great art - but surprises are sometimes thrown up. A lot of the rest, though, is very good. Many of these artists have developed their scripts into intensely rhythmic, eye-catching styles that create great spatial complexities. They're good to look at. It's an interesting idea for a show, though, and worth a look.