[maltyr]

Games actively train a player's "skill". I define the player's skill as the player's ability to use the mechanics in the game to meet the challenge the game is presenting.

The way to make a game more replayable, then, boils down to 3 things:

1) Make the game more challenging. This forces the player to change their approach to problems (because their old solution no longer works)

Multi-agent games do this by having a variety of opponents.

Single-player games do this by ramping up the difficulty, generally by making the execution requirements tighter. More complexity, or less leeway for mistakes.

Leaderboard-type games do this by using a "best score" as the goal. (e.g. Rhythm games, racing games, etc.)

2) Adding and/or removing mechanics that force the player to change their approach to problems. Again, this is either because the old solution doesn't work, or you must use the new mechanic in the solution.

3) Add randomness, mimicking either of the above. (e.g. Roguelikes/lites, deckbuilders, etc.)

There's also the possibility of extending play-ability by "creating new content". I think this isn't really "re"playability, since the generated content hasn't been "played" before, but procedurally-generated content and sandbox games have this sort of code-generated-novelty-as-replayability.

[orbital-decay]

3) Add randomness, mimicking either of the above. (e.g. Roguelikes/lites, deckbuilders, etc.)

Not sure that the randomness in roguelikes is just mimicking the challenge. Nethack is a canonical example of randomness adding to depth. The game is insanely random, but the mechanics are unbelievably deep and diverse, and if you are skilled, you can always avoid death in a myriad of creative ways unavailable for a newbie.

The downside of such a design is its combinatorial complexity, which is also apparent in Nethack, as it also allows plenty of "abusive" behavior. In contrast, DCSS devs aggressively cut features from the game to "streamline" it (aka simplify it enough to make the task of preventing abuses of mechanics easier)

This can be applied to anything skill-based that contain randomness or incomplete information, down to battle royale FPS games - the skill is in to use the knowledge and game sense against whatever the RNG (or a game situation) throws at you to get predictable results.