The Where in the World Game is part of the recently released Google Maps Labs, which you can find by clicking on the green flask at top of the Google Maps page. After you've enabled the Where in the World Game you'll find a link to it at the top of Google Maps.
Both games ask respondents to identify a country based on the displayed location. Where in the World picks a random location within a country, and country borders are not indicated, so some judicial zooming out is sometimes necessary to get your bearings. Country Bumpkin, conversely, indicates the exact country silhouette, and ensures the correct initial zoom to see the entire country.
Where in the World adds a time aspect to the quiz, so faster responders receive a higher score. This would be a worthwhile addition to Country Bumpkin to reduce the possibility of cheating by checking other map sources.
Country Bumpkin asks questions in increasing level of difficulty, whereas Where in the World appears to operate on just a single, easy, level. It also sometime asks about the same country repeatedly in one session, which is not ideal.
Finally, Where in the World maintains a high score table for your computer, which is a good incentive to play again. Although I'll be mostly sticking with Country Bumpkin for the moment, I look forward to future improvements from Google.