http://www.mangareader.net/638/zetman.html http://www.mangareader.net/terra-formars Supposed to be pretty good I haven't started it. http://www.mangareader.net/btooom http://www.mangareader.net/322/code-breaker.html http://www.mangareader.net/400/freezing.html http://www.mangareader.net/530/the-breaker.html and part 2 http://www.mangareader.net/the-breaker-new-waves http://www.mangareader.net/485/claymore.html http://www.mangareader.net/1407/variante.html If you go to the end of any manga series on that site and click next page on the last page it will show you a handful of manga that are similar not always accurate but I have found a few worth reading with it.
If you like .hack There was a Korean manga with a MMO style manga. I forget the name of it, infact I dont think I even finished it but I know I enjoyed it very much.
these are on my list..Ive read Saga..love it The Unwritten By Mike Carey and Peter Gross Saga By Brian K. Vaughan and Fiona Staples The Manhattan Projects By Jonathan Hickman and Nick Pitarra
Lets be honest, nothing will ever live up to Berserk unch: That being said, if your into "Samurai, way of the warrior, etc style" then... Vagabond (Artwork is close to, or on par with Berserk... starts off kinda slow) http://www.thespectrum.net/manga_scans/?preview=manga_Vagabond Blade of the Immortal http://www.thespectrum.net/manga_scans/?preview=manga_Blade-of-the-Immortal Vinland Saga (Vikings, nough said) http://www.thespectrum.net/manga_scans/?preview=manga_Vinland-Saga ( All 3 of which are Berserk esq. Gory, decent enough stories, nudity... other adults themes >.> They're all kinda mainstream though, so im sure you've heard of them before )
I highly recommend Bastard!! by Kazushi Hagiwara. Started in 1988 and is still going. http://www.mangareader.net/292/bastard.html You wanted something more "adultish"