I'm finally getting around to Psychonauts too! I've had a PC copy of Psychonauts (5 CDs!) that was given to me by a buddy 3 or 4 years ago. All the Brutal Legend publicity reminded me I had Psychonauts up in the attic and I'm finally giving it a playthrough.
What I didn't like: The first 4 hours... I'm not a huge fan of the character design and the start of the game is cutscene city. But it grew on me after that, and once I hit the Goggleor section I was hooked. I'm nearing the end and although I'm not crazy enough to go back and find *every* last collectible item, I really enjoyed it.