well, in the beginning it's not that dark, just a bit dark and humorous. If I remember correctly, halfway the darker stuff starts popping up leading to a finale that's also pretty dark.

I've heard it's not as dark as ergo proxy, but still enjoyable to lovers of the genre (I've only watched a few dark animes (seeing as I've had no-one reccommending them to me) so I'm not the best judge)

(and I know, too much use of the word dark in such a brief post, but I'm tired...)

XD Well that sounds fine to me..it doesn't need to stay "dark" the whole time.

I haven't watched Ergo Proxy though i've heard of it.

I've only heard rumours about it (sounds ominous doesn't it)
I haven't watched it.

But then again, I'd only heard about elfen lied in rumours as well and that wasn't that dark at all... (it was nice, just not what I expected... Ibara no ou was much darker, though I haven't watched the anime, the story was darker)

I've seen Elfen Lied. I found it sorta dark but mainly violent. I've never heard of Ibara no ou.

it's not dark at all, just violent, like you said.
King of thorn (Ibara no ou) is a little darker storywise but mostly the setting's darker.
The violence is also a little lessened than what elfen lied is (though as I mentioned, I've not seen it, just read the manga completely...)
Ibara no ou has a storyline that twist more than Elfen lied. It's also less predictable... (at least to me)

Sounds interesting. I like when the story isn't super predictable.

The anime for Elfen Lied seemed too short and rushed which is a shame. I'm sure the manga is better.

It's usually better but it's more convenient for me to just watch anime.