Apocalypse World does this neat thing of boiling down the "rules" for the GM (or MC) into an Agenda (what are you striving for), Principles (what you should and should't do) and Moves (how you do it, in the game, with the game's fiction).
Agenda is simple. It's just what the GM is supposed to be going for, what his goal is. Moves are wildly different from game to game, but they mostly draw from the same pool. Moves are stuff like "Throw ninjas at them.". Whatever.
Principles are the most interesting, because it's the first time in history (I think) that GM advice has been turned from just vague advice and a "you're supposed to know this by yourself"-approach into a concrete set of points you're supposed to follow.
Sage LaTorra has done a great series of posts, trying to distil the general vague advice of D&D editions into sets of Principles. Here they are:
The Moldvay Set
and the comparison
I think another interesting point of comparison would be 3E-to-Pathfinder. It would be intriguing if there are any differences at all, and if so, what kind of differences.