How close is it to the original gameplay-wise? I think it's more likely that I'll buy the GC version before the 3DS one.
Don't take my word on this (since I've only watched a friend play it), but it seems that Dark Moon, like I mentioned before, takes on a more puzzle-like gameplay style in comparison to the original. So if you've ever played a LoZ title, then you'll find the game's play style to be quite familiar, requiring for you to really think to solve puzzles and progress further in the mansion. Dark Moon also offers more than one mansion to discover, and the ghosts are entirely new. There also doesn't seem to be any humanoid ghosts in the game (rather disappointing to be honest), that, and the bosses seem to all be the same type of ghost. The game still closely emulates the original, however, but I feel that DM adds a bit more to the experience with the additional objectives like finding all 13 gems per mansion, and finding a boo for every mission to unlock a timed ghost capturing mission.
So in a sense, DM is pretty similar to the original, but adds more to the experience with new objectives and slightly altered gameplay. Getting the original Luigi's Mansion would probably be a better idea, regardless, so that you can acquire a better perspective of the series, rather than just jumping into the sequel like I did. :B
Edited by Manny T. Starr, 31 March 2013 - 07:51 AM.