Well, I've seen all the basic gameplay rules I really care to. They all boil down to about three basic mechanics with a thousand special rules lumped on top. I hate special rules. I prefer to layer gameplay mechanics instead of making special rules for a single gameplay mechanic.
One of the things that this allows is for a rule to control the way gameplay progresses - the pacing of the game, if you understand. It's more common in board games rather than tabletop RPGs. For example, in the Battlestar Galactica CCG, they have a "if your fleet gets too big, you piss off the Cylons" rule which makes for a definite shift in play between early and mid game. Similarly, in "Shadows over Camelot", the quests advance with or without you, which makes the end game usually a sprint to get those last few successes before the bad guys get their last few successes.
Indie tabletop games occasionally, very rarely, have a system for this. "With Great Power" has an explicit one, whereas "Prime Time" and "Rune" have one that is more of a guide rather than a layered set of rules. But these rules - or guides - make the game dramatic and fun in a way that is unique. I honestly don't think any game should be created without carefully thinking about the way it progresses from early to mid to late game.
With that in mind, I've been looking at the ways to make these progressions interesting, and I've come up with some basic observations:
1) Scarcity of Resources. Generally, as the game progresses, resources become more scarce as the players use them up. In some games, "resources" are literally tokens or cards or lives that are used to do things, but in many games the "resources" that get scarce are places on the board. Land, essentially, as the players (or other mechanic) fill it in.
2) Achieving New Modes of Play. Some games give you new capabilities as the game progresses, either on a schedule or in exchange for some resource wrangling. The opposite is also fairly common, with the new rules making it more difficult for the players.
3) Goal Changes. Some games put out new goals for the player. It could be done when an old goal is accomplished, on a timer, randomly, or when a player plays a new goal. Any way it works, this changes what the players are after and, therefore, their method of play.
4) Explicit Stages. The most likely method for a computer game or tabletop RPG, explicit stages carefully lay out a new set of resources and, often, new modes of play/goals. In its most common form, each stage is a new game with your starting resources altered by the previous game. However, in some cases a "stage" is actually only one part of play, changing only one or two aspects of the game when it switches.
5) The Hidden is Revealed. In any game with imperfect information, it is possible to "schedule" the reveal of that information. For example, in Shadows over Camelot, there is often a traitor. The game is largely about him balancing secrecy and effectiveness until the circumstances of the game essentially force a reveal. This is not like House on the Hill, where a traitor is invented at the moment of reveal. That's not hidden information, that's an explicit stage switch. I'm basically only counting hidden data that players are directly affected by even before it is revealed. Otherwise it's not hidden data.
#5 is a little iffy. There's something wrong with the way I phrased it. Can you think of any methods I didn't touch?
From these methods you can choose exactly how you want your game to progress. More is revealed about how a game feels to play by looking at it through these lenses rather than looking at the actual rules. Also, nearly all feedback loops are one of these rules.
For example, Chess is about killing pieces and controlling positions. The pieces are a limited resource that fades as the game continues, but they don't fade at the same rate, so a better player retains more pieces than a weaker player. That's a positive feedback loop.
Anyhow, food for thought. Comments?