An odd cross of RPG and adventure game, Penny Arcade is a great game for the price.
The good:
+ Great cel-shaded "hand drawn" visuals with excellent in-game animation.
+ Equally good, though minimal, sounds and music throughout.
+ Light, fun storyline with some good characters.
+ Straightforward gameplay allows you to pick it up and play it once in a while without worrying about remembering a story or puzzle nuances.
The bad:
- Combat can be a bit frenetic, as you have to manage three characters in almost real-time.
- Short -- hopefully the follow-on chapters will be closer to $10?
- Very linear -- I'd like to see future stories allow a little more free adventuring.
- "Level up" RPG elements are all automatic, making those elements almost meaningless to the player, particularly given the linear nature of the story.