What is a good mature anime?

Try Hellsing, it's a show about a vampire that fights other evil vampires. And sort of falls in love. How about Blue Seed it's about a sacred high school girl who can save the world but she has to be killed to do it. She falls in love with the freak(both in body and spirit)who tries to kill then save her. Dare I mention Cowboy Bebop? Have you tried Desert Punk? How old are you? Do you know of Hentai?