I think Luigi's Mansion as the main release title was a huge mistake, and is directly responsible for the miserable marketshare the GamCube now holds.
Like millions of other people, I bought the original NES for Mario, I bought the SuperNintendo for Mario, I bought the N64 for Mario. When the GameCube came out there was no cool new Mario game to go with it.

I didn't buy my GameCube until Mario Sunshine was released. I also didn't buy any other games that were released before I bought my Cube because by then they were old, and I knew new things were on the way.
Had I bought the Cube earlier (at launch time WITH Mario), then there are a lot of titles I probably would have picked up. As it is now, I only have 5 GameCube games, and don't plan on buying any more, unless something really spectactular comes out.

They screwed up, not in the hardware (which is amazing) and not in the software (which is amazing) but simply in the timing. Every new console NEEDS a flagship game to move the boxes out the door and establish the base for future software sales. Nintendo didn't have that. A game where you tediously chase ghosts with an oversized penis pump is not a flagship title.