The ruleset is DCC, but the important part is that they nail the setting feel. With a little crunching, you could transpose the meat of it to whatever you please.
They're great, and I'm buying every release they put out. But I do kind of wish they reined in the excess a bit so they took up less shelf real estate. A three-volume set following a two-volume set is pretty silly. Goodman isn't exactly known for restraint, though; nothing compares to their Judges Guild Deluxe sets which are as large as reading the The New York Times...