On the Rain-Slick Precipice of Darkness is an episodic RPG-adventure game series set in a deranged comic-book meets-pulp-horror 1920s universe. Armed with unconventional weaponry and witty repartee, you join forces with the Gabe and Tycho, the crime-solving team of the Startling Developments Detective Agency to make war on bizarre enemies and solve the mysteries hidden deep in the sinister heart of New Arcadia.
From the hilarious and twisted minds of Penny Arcade creators Mike "Gabe" Krahulik and Jerry "Tycho" Holkins, legendary game designer Ron Gilbert and veteran producers at Hothead Games comes a 100% authentic and hilarious Penny Arcade experience.

From what I've seen of it so far, that last bit is dead on. The video game is truly effing Penny Arcade. (Either you get that, or you don't.) I'd really like to write something eloquent and insightful about it, but basically, it is the embodiment of the web comic, which also happens to be a video game filled with win.

At ~200 megabytes or so, it is deceptively tiny. ...but since the entire thing is either (and alternatingly) cel-shaded or vector-driven, it can be expected to compress well. (It also looks seriously pimp at 1680x1050)

Download the demo. You will see. (Oh yes, did I mention it runs on everything? Windows, OSX, Linux, and XBox360. ...and the system requirements are miniscule.)

On the Rain-Slick Precipice of Darkness, Episode One