Pokemon GO yesterday and played around with it briefly in the evening. Today was the first day I really had a chance to explore the game mechanics. The game is using the same backend as Ingress, which Chris and I played quite a bit a few years back.
The map is similar looking, but the play around capturing Pokemon (where you can have the Pokemon overlaid what you're camera is seeing) ads a whole level of complexity to the game. I can see why it's so popular so fast.