To be honest.. I completely enjoyed this game, if they made another and none of the game mechanics/basics were changed.. then I would still be a satisfied customer.
However.. it would not hurt if they were to make it a bit longer, and perhaps include more of a story with the ghosts. By this I mean, for there to be a plot involving the ghosts, rather than going room to room and vacuuming whoever is in it. I do understand that there was a short backstory provided on the ghost, however it really made no difference to the game. Perhaps there could even be more 'scare factor', or more mystery to it.
I'd like another one, maybe just fine tune a few apects and whatnot as all sequels should, maybe add some new power ups to the vacuum and some more backstory would be nice or even have some of the ghosts interact with one another somehow..
All your children are poor unfortunate victims of systems beyond their control, a plague upon your ignorance and the gray despair of your ugly life.
I hope that Nintendo will make another Luigi's Mansion eventually..
Hmm.. and I just thought of something.. what if in part of the story.. you were turned into a ghost and a ghost stole your identity by turning into you.. I am aware that it has been done before in other games, however I believe that it would be fun.. To wander about the mansion as a ghost..