The Hating Girl is about a boy who meets a girl with an arrow stuck in her head. How did it get there? We don't know, and the boy doesn't either, so he really wants to know why there's an arrow in her head, and starts to become friends with her.
That's basically all the storyline information you need. View The Hating Girl as a 'monster-of-the-week' kind of manga, it has silly little plots in each chapters, and it rarely gets carried over to the next one. Though it does one thing that most 'episodic' manga don't do, and that is to carry the feelings over from one chapter to the other. Progress between the girl and boy is slow, but sort of realistic. They grow on one another, and eventually fall in love.
In return for lacking any real plotline, The Hating Girl has got heart and charm. It's a breeze to read through, nothing getting quite serious, and if there is any drama at all, it'll be solved in the next chapter. That's what makes this manga so fun though, it's a nice read and you can just sit there and read it at ease. Of course, you got to have this kind of taste, otherwise you'll probably get bored and stop reading after a few chapters. Just like the manga Love Roma, this manga is slow but cute and funny.
I actually liked the art, it takes a bit getting used to because of its unique style, but it adds to the charm of the story. I'll take this artstyle over any generic shoujo style any day. Then there's also the ecchi factor to take into consideration. Like Love Roma, this manga can get pretty damn perverted, but it's still all innocent and fun, though those chapters do stand out like a sore thumb.
Anyways, The Hating Girl is nothing special, there's no real plot (aside from the question how the hell did she get an arrow in her head), but it's charming and cute, for that I give it a 7.5. Give it a read, you might find you like it.