TRENCHED Pictured: an explosion.

SOMEWHERE IN the near future, there exists a lecture hall full of students frantically scribbling notes. A thirtysomething professor stands in front of a chalkboard littered with pseudo words like "replayability," "incentivization," and "robopocalypse." The class is Game Design 101, and the subject is Double Fine's latest downloadable action game, Trenched.

Trenched is gonna be studied, at least in part, because every aspect of the game seems forged specifically to generate psychological addiction. Gameplay-wise, Trenched essentially boils down to "giant robots explode bugs en masse," but clever design touches elevate Trenched from a simple shoot 'em up to the game you force on people who don't "get" games.

For starters, the giant robots I mentioned are wildly customizable. Prefer a sniper rifle to that oversized shotgun? Strap one on. Feel more comfortable with four legs instead of two? Switch them out. Think urban camo is a bit gauche? Slap a solid black paintjob on your machine and you're ready for a night on the town.

Oh, but it doesn't end there. Each of these enhancements is customizable too. As in Blizzard Entertainment's beloved Diablo series, every time you kill an enemy you have a chance to find a special piece of equipment. Maybe it's a wildly overpowered chaingun, maybe it's a chassis that looks like the lovechild of a backhoe and Satan himself. It's all random, and the small chance that your next mission might reward you with an unstoppable killing machine makes it very difficult to stop playing.

Add to that Trenched's core gameplay, which is a mash-up of tower defense and third-person shooting, and the title's witty yet subtle sense of humor—Double Fine is headed by Tim "Psychonauts" Schafer, after all—and the end result is an endlessly replayable title whether you're solo or with a group of three friends.

Oh, did I forget that? Yeah, Trenched also offers four-person online or offline multiplayer. Apparently, that was the last notch on Double Fine's "How to Destroy Worldwide Productivity" checklist.