|Robo Rally the board game|
While it doesn't look like it has as many game pieces as Monster Chess, the game board itself looks considerably larger (That's Monster Chess in the background).
Each one of those game squares is completely LEGO and I'm guessing they're all 32x32 baseplates.
Now 32 x 32 baseplates = 1024 pixels and with 12 x 12 game tiles shown in the video that equals 147,456 pixels. While I don't think they used 1x1's for every pixel, that's still a lot of LEGO!
Steve's blog - http://teamhassenplug.blogspot.com/ has lots more detail about how it was made as well as plenty of great photos. Looks like it was a real hit at Gen-Con and Brickworld.
****Update from Steve Hassenplug himself****
Damien, the baseplates are actually 48x48 or ~330k 'pixels'.
If you look close, the board has an 8-stud 'warning stripe', so that's ~350k.
Including the entire boarder, (14x14x48x48) the whole board is ~450,000 studs, or 17.5'x17.5' or just over 300 square feet.
We estimate the tiles are 1/2 2x2 and 1/2 1x1, which means ~150,000 pieces.
Yes, it makes Monster Chess look small. :)