I never played the game back in the day, but always pondered buying it, and finally did so recently. It has some great moments that make it worth playing, but between them you have to wade through some - not bad, mind you - but certainly average sections.
The platforming is decent but not great, and the difficulty can suddenly turn from very easy to bloody hard (*cough* Meat Circus). But the concept of getting inside people's minds creates opportunity for some great worlds, and here Psychonauts fully delivers. Whether it's the brain of a grizzled soldier, a crazy conspiracy theorist, or a giant mutated monster, they all feel memorable and unique.
I also mention I didn't like the ending, It's not so much as a hint to a sequel, it could be the intro for one. But the sequel never came, so I guess the joke's on them...