It's a very innovative and engaging 3D adventure game with platform elements.  The characters, dialogue, and detail is above and beyond most other games that I've played.

And you can download a playable demo:

Psychonauts Download Links Page

The demo actually contains a surprisingly large amount of gameplay value.  It entails the entire first level of the game, which is pretty challenging.  It's a 400mb download so you'll want to have a fast connection if you're going to go for it.

The game isn't sold in stores ...

Here's a game I created a while back.  The premise is simple, move the smileys into their same coloured doorways.  Gameplay starts off slow and easy, but gets harder at each level.  See how far you can go without being overwhelmed:

Download The Great Smiley Migration


Instructions:

The leader of the smilies has betrayed his people and sold his loyalty to a chain of discount stores for the simple privilege of playing their mascot in TV commercials.  He's sold the rights to all the smiley ancestral lands for the ...