Im an adult and I like manga, but I am having a hard time finding new mangá 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 you deside yourself im a sraight man so i wouldnt relly know any thing on a dudes looks and its an adult mangá not hentai just relly violent

Hmmm... Higurashi: When They Cry is a suspenseful, sobrenatural 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 mangá that incorporates all of them either off the topo, início of my head). Hell Girl is pretty dark and has sobrenatural stuff in it. Pet comprar of Horrors is a dark mangá too and definitely shows the dark side of people. It's sobrenatural but set in modern times, and I think the comprar 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( yaoi lots of it if you don't like yaoi then don't read it)
thats all i can think of

There's a website that you can choose your genre's and find what your favorito Mangaka's mangas' are. You can also go on mangá procurar to find your favorito manga.
The website is:
link

On mangá Fox:

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

I recommend the following as animê (and I know you asked for manga...but you may like the mangá versions:

A Cicada in Winter (Fuyu no Semi): Historical, Long hair, yaoi amor 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 or Kya Kara Maoh: hot guys, some hot guys with long hair, fantasy, adventure, magic, warriors - archaic setting. Grows darker.

kuroshitsuji - historical magical fantasy, dark, supernatural, but no long hair.

If you look on
link
you'll find a huge amount of interesting yaoi mangas - there are a few historical fantasia stories with delicious guys and long hair ...and swords.... and you can look them up on Mangafox or google to read.

If you really like Kenshin but read it all and want mais you should read Samurai Deeper Kyo.

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

And I think you 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 amor intrest of the lad.
Its a very good all-around mangá that can be very funny and very serious.

Image from Demon Diary:

do you 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 mangá in my opinion.....
or the mangá Hell girl? you can find it on manga.animea.net i think....
or Tsubasa Chronicles?
or xxxHOLIC
or Stray dog? its pretty good but it ended too quikly.........
or um.... chibi Vampire? (im not sure if youll like it though..)

maybe chobits.