Psychonauts was less than successful in it’s time. Tim Schafer has said, when speaking with PSM3, that he would love to do a sequel if he could find a publisher willing to do it. He believes that the first game has gotten out to enough people by now that if all of those new fans bought the next one it could be a fantastic success.
I am personally a big fan of Psychonauts. I have very fond memories of pre-ordering the game and having it shipped to my house and getting into that crazy brain main menu.