What is Ingress? Perhaps the better question is how have you not seen it? Ingress is all around you, not so much being "played" as it is being "lived" day in and day out by millions of people. Chances are you know some of them, and chances are you've seen it in action. Felt it, even.
Ingress at its most basic is an alternate reality game (aka AR) that pits two factions gainst each other for control of Mind Units the world over. You're either among the Enlightened, or you're part of the Resistance. Portals are the key to the entire game, disguised as everyday objects all over the world. Portals can be linked together until a field is established, thus capturing the Mind Units within.
It's not that easy, though. It's a constant back-and-forth struggle between the two factions. What was once blue is now green.
Ingress really is a way of life, however. You'll find yourself places you never expected to be, among people you might have otherwise never met.