Marketing, unfortunately, makes all the difference when it comes to games. Grim Fandango didn't receive as much as it could have enjoyed, which largely accounted for its initial poor sales.
Another similarly awesome game that suffered the same fate is Beyond Good and Evil, which is commonly heralded on a similar level to Grim Fandango. I don't necessarily agree with that, but it comes pretty damn close.
Hopefully publishers won't make the same mistake with Psychonauts (
http://www.razputin.net), which as I'm sure you know has been in development by Tim Schafer and his cronies for a number of years now, and is due for release in one month. I doubt they will though, since Majesco seem extremely committed to pushing it into the limelight.