Double Fine Productions and Tim Shafer are known for making very curious games out of amazing ideas. Psychonauts is exactly about some idea. You have to get inside people's mind and help them fight with their fears or memories from the past.
We follow a story of Raz, who runs away from the circus and goes to the summer camp for Psychonauts - people with special abilities. They refuse to teach him but allow him to participate in "Basic Braining" course. When his talent becomes clear, he's being invited to an experiment. After receiving a vision, he realises that there's a sinister plan behind the camp and only he can save everyone there.
The game exists in two different worlds - a real one and a mental one. If the real world leaves no question about it, the mental world is one of the most interesting features of the game. Twisted minds, memories from the past and deepest fears is something you are about to encounter with. Having a number of abilities like telekinesis or invisibility will help you cure a person's psychological issue.