Some of my favourite examples of location-based gaming are almost direct mappings of classic games on to real-world locations. GPS Tron for example, takes the the virtual lightbike race of the original game and allows people to play out the game on real roads. Similarly Pac Manhattan overlays the pac-man board on the city grid of New York and challenges a costumed pac-man to avoid equally real Blinky, Pinky, Inky, and Clyde ghosts.
However, by linking in more closely with everyday life and social interaction, locative games can take on a much more addictive longevity. A great example of this is the Tokyo based game Mogi launched back in 2003. It challenges players to hunt for digital items from around the city. They are awarded points for each item they locate with their GPS mobile phones, and bonuses for collecting entire sets (of pixel flowers for example). The simple Mogi phone interface comes with a richer online environment where players can trade doubles of items, look at where other players are in the city and send them live tips.
[Mogi] is a good example of a style of entertainment suited for mobile devices. It’s very casual, playable on your way somewhere. It nestles in your every day life, rather than requiring you to change your behavior.