While I've yet to see an augmented reality game (or app, for that matter) that uses augmented reality in a way that feels like much more than a gimmick, it's cool seeing Lego embrace technology more. Anyway, the way it works is to buy one of the Lego fusion sets, of which three are currently available with one "coming soon." You build the bricks, which all seem to include the telltale augmented reality marker patterns, launch the app, point it at your legos, and you're in business.
The three Lego sets available now are pretty typical Lego and involve a race car, a medieval tower, and a town. I'm really curious what it'd take to fool the companion apps in to thinking you have the Fusion sets, as I bet it's just looking for the pattern of darker bricks to overlay the game stuff on top of. If you can get them in the right place, with your own Legos, it might just work.
Here's a video of it all in action:
It looks cool, and it must be awfully fun to be a kid now with all this kind of junk you can do with Legos. Why, back in my day we just built stuff out of Legos and played with the bricks themselves. Now, if you'll excuse me, there's some kids I need to shoo off my porch.