From the site:
Using Google Earth placemarks and web pages, we've created the world's biggest interactive game.
In order to beat the GameMaster, you must follow the clues and utilize the Checkpoint feature to move ahead.
Once you've beaten the first GameMaster, you'll advance to the BIG GAME of EARTH CONTEST where you'll compete with other self proclaimed super sleuths for BIG REWARDS!
A list of "big rewards" is not provided but a few of the pages mention that if you "win" you get an "unlocked" expert version.
Aside from that material and a basic tutorial, that's all the info provided. An email address is also included.
Team play is available and according to this page, "encouraged."
That's it. It looks like fun and one of these days I might give it a go. If you play, share your thoughts (good, bad, indifferent) in the SEW Forums.