It’s generally necessary to know what your audience want from your product, and a lot harder to know how to communicate that to the aforementioned audience. The promotional material for Team Fortress 2 is doing an amazing job at conveying fun :
First, the generic teaser:
Then it gets better.
Meet The Heavy:
Meet The Soldier:
It’s successful not just as a way of keeping interest (there are, presumably, going to be “Meet The…” videos for the rest of the characters) but as a way of making people want to play the game – ultimately, the point of any marketing. There’s no reference to how the game plays; the videos just make it look fun. Even I want to play a game made by people who can be that funny, and I’m currently struggling with New Super Mario Bros. for DS.