Im an adult and I like manga, but I am having a hard time finding new Манга that attracts andkeeps my interests.

berserk sounds like something you'll like its set in midevil times has magic monsters main character is not a good guy as for the pretty boy thing griffith the storys villen should be fine ill put a pic so Ты deside yourself im a sraight man so i wouldnt relly know any thing on a dudes looks and its an adult Манга not hentai just relly violent

Hmmm... Higurashi: When They Cry is a suspenseful, Сверхъестественное story. There is no hot guy with long hair and it is in the present, but it's very suspenseful. Beserk is definitely up your ally (and I can't think of any other Манга that incorporates all of them either off the вверх of my head). Hell Girl is pretty dark and has Сверхъестественное stuff in it. Pet Магазин of Horrors is a dark Манга too and definitely shows the dark side of people. It's Сверхъестественное but set in modern times, and I think the Магазин owner is pretty hot...

(image is hell girl)

hmmm well some of these are aimed at teenagers but they may appeal
Moon phase
Vampire knight( this is aimed at 13+ but i think the age ranger goes from 13-32)
Chobits( it's okay but there's lot of explecite material yeah i know your an adult but some ppl don't like that stuff)
loveless( Яой lots of it if Ты don't like Яой then don't read it)
thats all i can think of

There's a website that Ты can choose your genre's and find what your Избранное Mangaka's mangas' are. Ты can also go on Манга Поиск to find your Избранное manga.
The website is:
link

On Манга Fox:

White Guardian (mangaka Duo Brand almost anything by her) Excellent.

I recommend the following as Аниме (and I know Ты asked for manga...but Ты may like the Манга versions:

A Cicada in Winter (Fuyu no Semi): Historical, Long hair, Яой Любовь story, dark.

Koutetsu Sangokushi - archaic, supernatural, dark, warriors, magic, fantasy. I hate machinery too and there is a teensy bit in this, but I highly recommend it anyway. Long hair.

Mirage of Blaze: dark, fantasy, supernatural, part historical(hot guys but little long hair)

Kya Kara Maou или Kya Kara Maoh: hot guys, some hot guys with long hair, fantasy, adventure, magic, warriors - archaic setting. Grows darker.

Black Butler (Тёмный дворецкий) - historical magical fantasy, dark, supernatural, but no long hair.

If Ты look on
link
you'll find a huge amount of interesting Яой mangas - there are a few historical Фэнтези stories with delicious guys and long hair ...and swords.... and Ты can look them up on Mangafox или Google to read.

If Ты really like Kenshin but read it all and want еще Ты should read Samurai Deeper Kyo.

Its not exactly the same as it seems to use is similarities to fool Ты with one of its major plot twists.

And I think Ты would like Demon Diary as it is about a kind and gentle boy who becomes the successor of a Demon Lord.

The person who shows him the ropes (almost completley unsuccesfully)
has long hair and is basicly a Любовь intrest of the lad.
Its a very good all-around Манга that can be very funny and very serious.

Image from Demon Diary:

do Ты read manhwa as well? Because I know one it's called crazy girl shin bia ... historical, and guys with long hair *not to mention hot). BUT the heroine is kind of annoying (for me).. well she's pretty not cute and very gangster like .. no manners and such but not dark.

how about FullMetal Alchemist? its an awesome Манга in my opinion.....
или the Манга Hell girl? Ты can find it on manga.animea.net i think....
или Tsubasa Chronicles?
или xxxHOLIC
или Stray dog? its pretty good but it ended too quikly.........
или um.... Чиби Vampire? (im not sure if youll like it though..)

maybe chobits.