Claymore can get pretty dang dark though, esp that part with the Awakened Being and Jean. They both feel pretty firmly entrenched in the gothic fantasy genre or whatever it is exactly.
Of course probably not the same level as Berserk, in terms of the intensity. Yet I just must deduct points for those helmets

*Shudders*
B-but I liked Griffiths helm 
Claymore can definitely get very dark. Both it and Berserk are very similar in how they handle the demons/yoma or w/e concept since both essentially come from humans who have pretty much gone too far and have become twisted creatures of darkness, with a touch of their human sides still added in. I like it because all the demons/yoma are unique, and quite often you can see their human aspects just very much twisted (much like a certain other anime which I love to death which will remain unnamed for spoiler reasons, but I'm sure you can probably figure out which I mean
)
The thing with Berserk though is many of the panels are just so extensive that I could just stare at them gawking for a while
Example:
The other thing, and I'll understand if you don't quite believe or agree with me here but I feel Berserk can be quite (I hate to use this word, but I do honestly feel this way) profound at times. It's one of those series that can have moments of genuine beauty, and filled with emotions without the need to actually even say anything or have some giant twist. It has those little moments in which you can see the good in humanity despite the dark nature of the story, and those moments are infact only enhanced by the darker aspects of the story Imo.
The other thing Berserk does which personally resonates with me is playing on the raw sense of wonder and fantasy, which are themes that I am highly drawn to. It shows both the darker and horrifying aspects of it as well as the good parts.
Mmm sorry, talking about Berserk gets me rambling quite a bit as Sim knows.