My Take
This is a very engaging game that helps kids learn about the states. Some of the facts are pretty random, but the overall effect is that they end up generally more knowledgeable about our country's geography, history, and nationality. There is a free sample but the full version game is cheap and worth buying for the full features, which include the ability to "earn" all 50 states and play mini games that reinforce geography and speed.
How I Use It
I use it primarily as a motivational tool. I like to reward kids for good, on-task behavior by giving them more opportunities to learn in fun ways. Because they like this game so much, it is a good incentive for them without wasting time or money on non-educational rewards. Students who complete their classwork in a focused, timely manner can play Stack the States in their earned "spare" time. The geography learning is a definite plus because that often ends up at the bottom of the priority list in my special ed classes, so this way all students have a chance to become more well-rounded in their social studies knowledge. They need to answer the questions correctly in order to get a state to add to their stack, so while they feel like they're playing a fun balance game, they're really paying attention to the state facts and remembering them for future rounds. As they win rounds and add states to their maps, they reinforce their recognition of the U.S. map.