This was the grand sweepstakes prize as part of a Modern Warfare 3 promotion. When completed in 2009, the screen was the world's largest, with over 20,000 square feet of HD display.
Playing Modern Warfare 3 on it looks mental.
The above pic gives you a good idea what that was like—the short clip gives a better one.
For some reason after watching it, I have the urge to drink Mountain Dew. Not sure why.