All right, for a long time I only had the first volume but when I went to stay with a Christian friend for a week I got to read up till 12! (minus one or two she had missing in her collection) So this is my opinion after reading all of those so far--
I am in love with the series. It definitely ranks as one of my favorites, even from the very beginning. I'm fond of the art itself.
It isn't just the typical badboy-goodgirl complex to it for me, it goes much deeper. Kira opens up through the series, learns to love, to be happier, better faith in herself (as she's a lot more insecure in the beginning). There's reasons why she is the way she is and how she grows.
Rei's had a pretty hard life, and though tough he gets a real compassion and love for Kira. You see his "hard core" change. I especially love Rei's growth throughout this series.
It's a drama-romance and not much fluff or nonsense. It isn't just prolonged through so many volumes but brings the epic story to life at the right pace. There's more intracacies and tough situations they have to face and relationships with friends and especially family. I won't give any spoilers.
As for question of content... I can't recall anything glaring. There's references to sexual relationships (more true-to-life though and not tasteless like a lot of anime/manga out there; I believe they do end up sleeping together way nearer to the end say aroun volume 10--I had to skip one volume there which I can't rightly verify for, but I don't think there was anything too graphic in the part I read), Rei is a bit reckless and there's a lot of character digging which sometimes edges on morbid, but there's always that hope which perhaps intrigues me the most about it.
So if it seems like it would interest you at all, I definitely recommend the series.
--star
and laugh a lot 
sorry but it might have answer something or warned you not to buy that vol. ^^ or read it if u don't want to. I love the first vol. is very funny and sweet. 