I enjoy Ghost Master a lot, and my wife adores it. It's not incredibly deep, but it's a lot of fun balancing the various ghosts, figuring out how to unlock the hidden ghosts, playing through the same levels with different combinations, etc.
It's not particularly hard - tenacity will eventually get you through every thing. But it's fun, and has a great art style. It could have used a few more unique levels, with goals like scaring only a set of people, etc, but it's a heck of a lot of fun.