Rich Carlson has a Gamasutra essay suggesting that games should become even shorter, and uses his ‘beer and pretzels computer game’ Strange Adventures in Infinite Space as their textbook study. It’s an interesting read, and discusses in part how lots of people are trying to make epics no one finishes, and how more people should be trying to make games more like Nethack. He estimates the average SAIS game lasts 20 minutes.

Replayability is a huge part of his argument. I’m not sure I’d factor length into a game’s replayability – Civ 2 games can be hugely long, but are infinitely replayable. Replayability, in my mind, ties directly into Raph’s Theory of Fun, which suggests that a game is fun as long as the pattern used to beat it remains interesting.

Civ is replayability because you’re applying your learning to random maps that escalate over time. Myst is less so, because once you know how to beat a puzzle, solving it again isn’t more satisfying. Adapting the pattern to solve new problems is interesting. Repeating the exact same pattern — not so much.