Games create situated learning, where the player learns and applies the learning in relevant contexts. These contexts might be real-world or a fantasy. The situated learning is engaging, and requires more than just absorbing content. In order to level up in the game, players must apply and solve problems. Much of our traditional instruction does not do this.
Moreover, in a bigger picture there are many ways to gamify learning by applying the game mechanism into learning processes. Carlton Reeve had created a series on how learning theories overlap with games, he also composed a table of how game mechanics relate to the ideas about how we learn.
By using and combining various definitions of game mechanics (Wikipedia, SCVNGR & Gamification.org), it is possible to map how dynamics correspond to the various learning theories. This is not an exact science but does suggest which mechanics can be used to encourage particular ways of learning.
Of course the risk with any sort of exercise like this, is that it becomes formulaic and is wrongly perceived as a rule for creating “learning” games. I don’t believe that is the case. Every game needs to be looked on a special case: as soon as you try to bottle the essence of play, it tends to evaporate.
Check out the correlation table from him here: Game Mechanics and Learning Theory, it’s a nice overview and an interesting perspective.