I’ve been reading Grognardia which is all about old school gaming. He mentions OD&D a lot. It occurs to me that we can just replace OD&D with M20 and skip all the nostalgia (because I certainly didn’t play D&D in the seventies).

It’s a philosophy of game design and game play that emphasizes loose rules, the sovereign authority of the referee, and player skill over notions of “balance,” “story,” or “fun.”

Once we accept that, then the following essay is probably of interest: Quick Primer for Old School Gaming by Matthew Finch talks about the difference between running a very old edition of D&D and more recent editions. I think the essay is just as interesting for M20 players.