"A Journey Through Middle-earth - a Chrome Experiment" is what it's called. As to what it actually is, I do not claim to know. Something digital - maybe a game, maybe a "Google Middle-earth" deal. Most of the comments about it on Facebook are just people arguing about whether you should say "autumn" or "fall." (The correct answer is "get a life." Being super-nerdy about the calendar when there are video games out there to debate is just a waste)
Watch the trailer after the jump, then tell me in comments what you think it is. And why it's browser-specific. Hobbits and wizards aren't generally down for specificity like that.