I've been pondering again -- rather pointlessly, I know -- about just what divides "Old School" RPGs from "New School" RPGs.
And once again, I'm coming up with a conclusion that points more to the players than to the rules systems presented in any rulebooks. Of course, the rules are connected, and can serve to reinforce what the players expect out of the game. But I feel that what's actually written on the page is a lot less important than how the players (and I suppose I should state here that when I'm using players in this little essay, I'm including Game Masters/Referees) interpret and use those rules.
First off, we can pretty easily say there's no specific 'cut off date' that divides games. We can't say that everything after 1989 is new school, or everything before 2000 is old school, or anything like that. The existence of the retro-clone movement has created neo-'old school' games recently. And some of those games created back in the 70's/80's definitely don't feel like what I personally, at least, consider to be that old school feeling.
Second, it again really falls on D&D's shoulders to be the benchmark by which other games are judged. It's the first and most popular RPG, and the changes in its various editions show a lot of adaptations of, or reactions against, innovations and player desires in other games. And those other games are often adaptations of or reactions against the current version of D&D on the market.
Third, and most importantly from my perspective, is that there are people who can adapt any rules set to suit their preferred style of play (as evidenced by the recent "I'm with D&D...any edition" internet badges out there). For many players, the real fun of an RPG isn't so much in what rules you're using, it's in that spark of creativity and shared imagination you have when the group you're playing with are all helping feed each other's shared imaginings. Yes, there are some people who get bogged down in rules minutiae and love the mental challenge of it.
The real breakdown between Old and New Schools, I'm thinking, is completely based on what the players are expecting out of the game. And it's got a lot to do with how well a player accepts limits on their character's potential. This is not about power gaming, but it is about being able to embrace the sub-optimal choice or to embrace the unlimited potential.
For Old School players, not every character created needs to be able to achieve the maximum potential for 'power' under the rules. If you get lucky, you might be able to create Luke Skywalker or Elric of Melnibone, but you're still willing to play as Fatty Bolger or Napoleon Dynamite. The limits imposed by the game are there to make those powerful characters feel special. Not every character is supposed to achieve the maximum potential under the game rules. And finding the best way to play that sub-optimal character is the fun of the game.
For New School players, it's important that any particular character have the potential for the maximum development. You don't need to get lucky, you just need to make the right choices and you can have that power (eventually). No one needs to get stuck with an Elmer Fudd unless they purposefully choose to play him. If you choose, you can be Gandalf. (With an implication that you'd better play Gandalf, because Elmer Fudd won't be able to pull his weight alongside John Carter, He-Man, and Cloud Strife).
So basically, if the game has 'balanced' classes, or a completely selective skill system, or a group's house rules allow repeat mulligans or for selecting options rather than rolling randomly, that's New School. If the players take the limits of the game and the results of random character creation and just roll with it, that's Old School.
Feel free to rip this analysis to shreds in the comments.