Theatre differences…then & now
I think that the primary differences between comtemporary theatre and Greek theatre would be the theatrical event that these Greek plays created.
I believe that in Athens the theatre was an important event where all the local dignantries all showed up and was the main form of entertainment for the Athens population. In this way theatre provided an important function in the community.
The audiences would be active and responsive (like a modern day football crowd?), and the audience as a whole would be emotionally very high.
The theatre was also a pageantry of patriotism that consolidated the nationalism of Greece