No offense to the fans, but I'm sure its mostly appealing to the same crowds who obsess over things like Cowboy Bebop, Big O, FLCL and No More Heroes. It has a similar art style, quirky design and 'adult' themes.
The game I'm confused about is LA Noire. If anyone but Rockstar was releasing the game, and it didn't have a multi-million dollar ad campaign, I bet people would completely ignore it for being a 'Boring Detective' game. Not that I think that way and I'm kind of interested in it. But I still don't see how it has this massive fanbase even before it releases.