What can I say, Valve was nice enough to include commentary tracks for all of their games, and I can't help but comment on it.

So the topic du jour is Team Fortress 2, released after all these years. (I have some things to say about Episode 2, but they'd be spoilerific, so I'm going to hold off for a while.) For anyone not familiar with TF2, it's a multiplayer only team-based shooter (red players vs. blue players), where each player picks one of nine distinct player classes to use for the round. The way the game plays changes depending on what class you're playing as.

Most of the commentary isn't really applicable to ARGs, unfortunately, but there was one bit that really stuck out at me. When they were designing the different classes, they realized at some point that it was nearly impossible to get an entire team to work together, as everybody had their own personal goals they were trying to achieve. Their solution to this was to build each level to encourage pairs of players to work together.

This is a good idea for designing almost any kind of multiplayer game. You can never expect full cooperation from your players, but you can expect small groups with similar goals to band together, and you should design with that in mind.

In an ARG, you might have a lot of small puzzles that all fit together into something more when they're solved. When that happens, the community feels pride at how they all worked together to accomplish a tremendous feat. In reality, of couse, they didn't work together at all. They worked individually (or in small groups) to solve smaller problems.

Perhaps the most important game design decision you can make is deciding how you want the players to play your game. Once you've figured that out, a lot of the remaining design can be deduced by asking "does this help the players behave the way I want them to?"