This is a 60cm tall replica of the engineer's sentry gun from Team Fortress 2, created from hundreds of LEGO bricks. ZaziNombies did a good job on this one, and the mounting doesn't even look like LEGO.
Now do the level 3 version of this with the twin-mounted gatling guns. That would look badass.
LEGO Sentry Gun - Team Fortress 2 [YouTube]