Luigi's Mansion was my first game on the gamecube, and despite what anyone says, it is a classic.
At the point of this game's release, Luigi's role in any game was highly limited. He was originally just a negative image of mario's sprite on the original games. Unfortunately for him though, he would always be the underrated sidekick. Much like Robin and Batman. Of course, what happens when he gets his own game--not to mention a game that is almost entirely original in concept (yeah, they took a bit from Ghost busters, but so what?).
It's certainly a dark mario game, but there's an undeniable charm that comes with playing this game. Not only is it technically fantastic, the game places characters in the game that have real depth. You see how each ghost interacts with each other. Their weeknesses, their strengths, their desires. It almost makes you feel guilty when you finally catch it in your vacuum.
Of course, the game doesn't get all too hard, but it can get frustrating at times. Catching all the boos in the game is certainly hard--especially because they can jump floors. The good thing though is that they'll eventually go back to their original hiding spot if you give them enough time.
Great game, classic, highly recommended if you have any sort of access to a gamecube or Wii--even if it's your friend's.