As an Anime fan, I give everything a chance. So I picked up HellGirl and thought, yes, this looks interesting, innovative and well drawn. And, well, it is, but what annoyed me about HellGirl was its serious lack of Plot, I watched about 12 Episodes of the Anime and noticed it suffers heavily from 'Monster of the week' syndrome even though the main characters are the closest things to 'real' monsters. The episodes didn't go anywhere and at 12 episodes, showed no real sign of change.
This Anime is good for showing the difference in right or wrong and provides moral, but seriously why would you send someone to hell and enter a contract to send yourself to hell to as the end deal? Surely you would just kill them yourself (if it bothered you that much) and hope that you don't end up going! I mean damning someone to hell for stealing a cake recipe as one episode shows... Yes, a cake recipe (already seems like they are running out of ideas)... Ah, well, maybe I'm being too skeptical, but it's just a tad weak :( which is a shame, because the idea was good.
Oh and some of the Animation is over played, when HellGirl is called, every episode, the exact same Animation is played for around 3 minutes, becomes monotonous if you are watching the episodes one after the other (you may not notice it if you watched one a week). All in all, I would not buy this Anime, there are far superior on the market. :)