Angry Birds. Just in case you've been living under a rock for the better part of the last decade, Angry Birds is a mobile physics puzzler where you catapult birds, presumably angry ones, into pigs' hastily (i.e., poorly) built homes. Having grown far past a mere mobile game since its release, being the subject of hundreds of merchandising deals, and even getting its own theatrical release, it has evolved to become something much bigger than intended.
Much like the XCOM concept, Angry Birds AR would utilize custom maps created from your own surroundings. Imagine creating an Angry Birds map in the park. It'd not only be massive, but it'd also potentially be rife with interesting obstacles. In addition, you could use a smaller area like a kitchen table for a less cluttered environment that would offer an easier time.