Hmm well we do not actually have any definition for genres, and people just pick whatever and they do get changed a lot because people have different ideas about things, or are using different references. For a quick example, GameFAQs calls Jinsei Game a board game but Mobygames has them as strategy. Yes even in our genre list, party is not an invalid selection for these.
I think that we should only add genres for things that are missing, and not try to delve too deep into sub-genres, such as "board game" being a division of "party"... We would rather have the sub-divisions of "Sports" before that I think, as there are many more games that need that type of separation.
Light Gun Shooter is an example of a genre that does need to be expanded upon. For the simple fact that there are many Wii/PS3/360 games that people try to attach Light Gun Shooter to, and the problem being is that those consoles or games do not actually use light guns.