What are the best plays you've seen never?

Tamburlaine the Great parts one and two uncut by Kit M
The Spanish Tragedy, or Hieronimo is Mad Again by Kyd

True, but plays have a certain reputation, so you often have a good idea of what is potentially great that you haven't seen. It raises many interesting questions, though. I have been going to plays for 30 years, the first 15 in London and then in the west with a few trips to the capital per year. I did feel after 15 years in London that I had seen pretty much everything. The most highly-reputed play I've never seen is The Critic by Sheridan and if I try to rack my brains I can think of Aeschylus' The Persians, Goethe's Egmont, Buchner's Danton's Death, Lorca's Yerma (to be remedied later this year) but not much else. Which suggests that there are far fewer great plays than great novels...I read a lot but there are dozens of highly-reputed works of fiction I've not read.  It's true that many novels take a lot longer to read than plays do to watch - you could probably see the whole of Shakespeare's History plays in the time it would take to read Bleak House, for example.  But given how often one sees the same plays again and again, I suspect the theatre canon is much smaller than the fiction canon.