I say "genre", but it is more like "target audience". I like it because, in some way, it is more broaden.
When you get a Shounen for boys, you know there is probably going to be action/adventure, like Naruto, Bleach, Dragon Ball, FullMetal Alchemist, D.Gray-man. But Death note and Bakuman are also Shounen.
In Shoujo for girls it is common to have more light stories, a lot of times there is a romance focus, Ouran High School Host Club, Maid-Sama, Fruits Basket are Shoujo manga. There is also Mahou Shoujo, that are those with magic girls fighting, like Sailor Moon or Card Captor Sakura.
Seinen for young men and Josei for young women are more mature, not because sex (sometimes yes, but not always), but darker stories, and usually more Slice of Life. But Josei do have more focus on love, and is usually more like Slice of Life, while Seinen is usually more violent.
But they also have things like hentai porn, yaoi gay men, usually for a feminine audience, and I guess those are genres.
Sorry for all this text >< I know these genres are too "animeish", but it is just an example, I think broaden genres may be helpful. I know that if I had to choose a genre for End., seinen would be appropriate, even though I do not focus it on a male audience.
Oh, yeah, you should totally add a "dark" genre.