UPDATE: full walkthrough video below. War never changes. War has changed.
I'm still downloading this, but I'll point you at it while we all work out what it is. The origin: a tweet from EA reading "Stay Frosty @Bulletstorm fans. Download a FREE version of the most epically epic FPS ever: Duty Calls." The destination: TheDutyCalls.com, a 765Mb download, a whole lot of cheeky references to Call Of Duty, and the below video.
BUT WHAT IS IT? I'll tell you if this bloody download ever finishes. 765Mb? This is surely more than a cheap pun...
I see what they did there.
CliffyB has chimed in too, claiming "Wow. I'm blown away. This game will redefine military shooters for years to come." Those jokers.
Get it here. See if you can work out what it is before I do.
Edit: And here's the full walkthrough. Made me giggle, it did.