This game is nothing about the webcomic duo, but it does include the webcomic's oft-kilter and graphical humor. It features a very different version of the duo, specifically a version which lives in a fictitious world where the occult is quite real.
Most of its presentation is provided through comic panels, not unlike the ones used in the webcomic. However, it is worthy of note here that Mr. Krahulik is not directly involved in the graphical designs, though his art-style is definitely there.
Much of the game's graphical designs relies on cel-shaded graphics, which do its best to maintain contrast between objects as befitting a comic while trying to portray the griminess of the occult.
The animations of combat can be quite entertaining, especially those of the player characters. For example, one of the player characters (namely the one which the player creates) uses a rake for aggressive purposes.
There is quite a lot of quick-time events though in combat though, thus making player reflexes a part of the gameplay, for better or worse. There are also elements of luck, e.g. critical hits and misses.
There are no voice-overs, but the lines which characters deliver would be quite satisfactory to fans of the webcomic. In other words, some characters, especially Gabe, are vulgar, while there are others, such as Tycho, who are rather wordy and pedantic.
However, a third of the dialogue - half of this being those of the main character's - is just lacking in Penny Arcade humor. One example is the player's attempts at rankling the Mime Lord. Of course, it has to be mentioned here that Jerry Holkins was not responsible for the entirety of the writing of the game.
The game makes a lot of references to the webcomics, such as the mostly forgotten eggplant that was shaped like Abraham Lincoln's head (with top-hat) and the references to hats.
Overall, this game is not fan-service - far from it. There are more than a few references to the webcomics and alternate-reality versions of characters, but the game seemingly stands on its own - and for the better too.