Ages ago, I remember it well, I was a front end manager at the neighborhood supermarket during my freshman year of college. The woman who worked the night shift me was a retired English professor. We got to talking about Shakespeare (shows how long my geekery goes back, I guess) and King Lear came up. She said, and it's always stuck with me: "If the entirety of human civilization were to die out tomorrow, all evidence of its existence erased save one thing, that one thing should be King Lear." I found it a powerful endorsement, to say the least.
Allison Croggon's review of Peter Brooks' King lear is damned near art all by itself: "...it seems to me that when I say something is a masterpiece, I mean that its achievement is not that it rises into some lofty empyrean sphere where history no longer exists. It’s a masterpiece because it does the opposite: because it makes a gesture so potent that it seems to draw all human experience into its gravity, because it reaches deep into individual and collective memory and hauls experience, naked and bloody, into the present."
Go read the whole thing, you won't regret it.