gamelength

Ninety minutes has become a bit of a benchmark, but it really depends on your game. If you want a game with mass-market appeal, I think, the shorter the better. I usually try to shoot for a playing time of an hour for my board games, and 10-15 minutes for my card games. In the end, just go with whatever suits the game. If you're designing a game that turns out as a deep, 2-hour strategy game, than so be it.

Same goes for short games. When I started designing Liar! I thought it was going to be a 20-minute-or-so game. While developing the game I kept chipping away elements, and simplifying the game, until the playing time of a single hand became only a few minutes, because that is what fitted the game best.