Depends on what they like in theatre, and what they value. I'll often add things into the description to draw attention to thinks I know the person will appreciate.
For my parents, I might say "It's a retelling of two greek myths set in 1930s New Orleans" because they don't know any greek myths and if I don't mention they atypical setting, they're going to be saying "Well why does it look like that if they're supposed to be in Greece". It's a primer to expect the show to be a bit more loose and metaphorical.
For my more radical or literary friends, I'll mention the ecofeminist themes, and the championing of workers rights and non toxic masculinity.
If I think the person knows any greek myths, or if I suspect they would value knowing it, I'll mention the myths by name and go through the traditional version if they want me to.
But a good general synopsis is "Hadestown is an adaption of the myths of Hades and Persephone, and Orpheus and Eurydice, set in 1930s New Orleans. Are you familiar with the myths? Do you want to know them?"
Def respect if people want to go in blind, you don't NEED to know anything. But I do think the show is best when you know the myth ahead of time. When I saw the London production, they handed out a detailed synopsis ahead of time, to read while waiting for the show to start. The tradition in Greek tragedy is for the audience to know the whole show ahead of time, some believe that is necessary to achieve proper catharsis. But depends what they value.