Anyhow, GSH smells like rotten eggs because it is a thiol. That means it has several sulphur atoms in its molecule. Even a teeny weeny bit that oxidizes will smell that way. This is the same principle that is used to odorize your natural gas by the gas company. Even the teeniest amount that oxidizes in the air will smell like rotten eggs.
But in the case of GSH, yes, something that smells so bad can be great for you!