There are many title already recommended by previous poster on this thread, so I'll just add a bitAomi wrote:
I probably read like only one manga that wasn't even finished so I'm new to all this.
I'd like some good manga recommendations for the horror/romance/drama genre; thanks.
For Horror try Hepatica, it's not a supernatural one so there won't be any ghost or some kind also It's already completed. Hi score girl is a unique one for a romance. The way it use classic games as one of the element of the story is awesome, provided you like games though.
Warning though, both of them have a rather "unique" art so try not to have high expectation on that part. (The story is still good though)