[njyx]

Agreed that you need a rewarding core loop and also one that becomes richer over time (more characters? more actions, more power, less power...). But, I think you also need a longer term engagement element beyond the core loop: being engaged with the goals of game. If there's only one (e.g. only one ending) then if you love the game you'll try to reach it at least one. If there are more you might be tempted to try them all.

Another thing that helps and isn't discussed much in the article is the "meta" game around a game. Especially if the game has liveops and new characters come out, there are events etc. Most by themselves probably won't make someone replay. But if there's enough new stuff and a community which is constantly discovering new stuff to do then that can spark the desire to play again.

[adamesque]

My favorite way for a core loop to become richer over time is when the loop has a very high skill ceiling the player can move through in a semi-controlled way. For multiplayer games, this means good matchmaking, but for other games this is layered in via optional challenges/achievments/bonus goals etc.

The stated goal of the game (aka reaching the ending) may or may not be along this path.