It's a regular platformer, and yet, it's also an artpiece.
While the gameplay is that of a normal platformer and it won't be as addictive as the one in other games by itself, the global atmosphere of this videogame is really charming.
The levels have an enormous variety of situations, all without changing the basic gameplay so nothing is half-cooked.
I say this because there's a lot of games that try to be creative by adding vehicle sections, or flying sections, etc, and in the end everything is bland.
This is not the case, every level in psychonauts it's awesome to look at,has amazing moments, and it will tickle the deepest parts of your mind.
How is this possible? Well, the game is basically set in other people's minds, so this results in a totally chaotic yet brilliant experience.
So all in all, is not a masterpiece, but a unique and fun experience.