What is the Burning Man Festival really like?

Is it REALLY just a bunch of hippies on drugs? I’ve been considering going to Burning Man for a long time, because I think the idea of radical self-expression is beautiful. And obviously I know a lot of the people are high the whole time. But would it be totally taboo for someone (like me) to go for a sober experience? Would I be shunned? What is it REALLY like?