Luigi's Mansion: Dark Moon.
I can't make up my mind. I really, really enjoyed the game, but it's missing something the first one had. The exploration was fun, as were the multiple locations (though in the original, the Mansion never really got stale) with varying environments.
The fact the game was level based (though technically the first one was too) felt odd, for some reason.
Still...I think the problem is sequel syndrome, of the variety that, when you love the original so much, it's hard for the sequel to match up. Still good, glad I bought it, but not quite as awesome as the first one.
Good stuff. And portable too, so I can bust ghosts with the convenience of a pizza bagel.