It's worth remembering that Dionysos does not figure predominantly in Greek heroic epic;as Burkert points out,the most influential portrayal does not come until the end of the 5th century with the 'Bacchae' of Euripides.Dionysos is an invader from the east,symbolising the tension between the West and the East,or the Apollonian and the Dionysian,that IS Hellenic culture.

I will give a fuller quote from Burkert regarding the mask,which should make his position clearer;

"Dionysian ecstasy is not something achieved by an individual on his own;it is a mass phenomenon and spreads almost infectiously.This is expressed in mythological terms by the fact that the god is always surrounded by the swarm of his frenzied male and female votaries.Everyone who surrenders to this god must risk abandoning his everyday identity and becoming mad;this is both divine and wholesome.An outward symbol and instrument of the transformation brought by the god is the mask.The merging of god and votary which occurs in this metamorphosis is without parallel in the rest of Greek religion.." [Walter Burkert,'Greek Religion',page 62]