I played Luigi's mansion yesterday at K-Mart, here is my review:

Graphics: I've seen N64 games with much better graphics

Gameplay: Very good, you get to call out Mario's name, dodge falling chandeleres, and the best part is getting to suck ghosts up with a vacuum, and actually funner than it looks, each different kind of ghost has a different amount of HP, you shine them with the flashlight until you can see their heart and then turn the vacuum on, then you pull away from the direction the ghost is moving with the joystick until it's HP is lowered to zero, the ghost drags you around, slamming you in to tables and other object which takes away from your HP and takes money.

Sound: Very good stereo sound, the mono is not that good so it would probably never be a gameboy game, and if your TV only has one speaker than you won't get full sound potential, nice gloomy Mario Bros. tunes and slamming boss tunes.

Ingenuity: It's a break away from all the normal Mario games, probably inspired by Paper Mario, it's kind of like Resident Evil meets Kirby.....

Overall it's a pretty good game, which ups my enthusiasm for the gamecube, Nintendo is dependable, not always big on graphics and adult games, but definitely dependable in the gameplay department.