The Romance genre. I'm surprised no company has pioneered and exploited this genre yet.
Games in this genre will be executed mostly like interactive adventure games -- but with several key differences. The new genre will capture the mostly untapped but potentially very profitable market of the hormonal teenage and lonely heart female demographics.
This genre will have no fighting. No combat. No weapon. No stats (because we all know maths and numbers make the ladies' heads hurt.) It will have plenty of (vomit inducing) "girl meets boy and they pledge undying eternal love for each other forever and ever but for some reasons they cannot be together" scenarios, with female lead characters and drop-dead gorgeous, ultra-sensitive male romantic interests that will gonna make real men puke.
The games will like a cross between adventure, exploration, and role-playing. They will have plenty of choices and dilemmas: should our "strong, empowered, beautiful" female protagonist (that's how all the girls -- even the fugly fatties -- love to flatter themslves) go with the ever-sensitive sissy boy who's torn between love and familial duty, or the rebellious bad boy with six-pecs who don't give a phuck about anyone or anything?
This will be a genre that no real man will want to touch with a ten-foot pole, but girls (and gay boys) will pour their money into it and become addicted. Whoever pioneers and leads the waves in this genre will make a shitload of money off those gullible females (no disrepect to all the bitches reading this.)
Don't any of your mutherphuckers steal my idea!!!