I've only seen the first few episodes of Hell Girl, so I can't review it that much. From what I have seen of Hell Girl, it seems interesting enough: a website called Hell Correspondence, which is a link to Hell. Here on this website you enter the person's name who you wish to see punished and Ai Enma will come to their soul to Hell, but there is a catch. When that person who condemned another dies, they must also come to Hell. So the series start such as that. The plot seems interesting and original enough with well thought of characters.
Unfortunately I can't really see where this show is going. Hopefully it will start to show of Ai's background. Aside from that though it seems like a good show. The background designs, are done well, especially where Ai lives, in Hell. They have given thought onto how to portray Ai's looks but not so much of her companions or others in the story. However they have used colour very well and differently which is a good thing.
Overall from what I've see, it is an intriguing show, which great taglines and would recommend people to watch it.