I first saw the movie and I liked it, not that much, but it was entertaining (I haven't read the manga, so I couldn't enjoy the movie like others did). People had told me that the manga was a lot better and that I'd probably enjoy the series much more.
I don't read manga so I decided to check the series out. The first episodes were pretty good so I continued watching them and... by the time I was half way through, I couldn't stop watching them. The story was so well made that it had absorbed me in an addictive way.
The music is actually pretty good too and... after purchasing the Special Edition, I have to say... the English Dub is horrible. Stay with the Japanese version with English subtitles, you'll enjoy it a lot better that way.
In resume: a must see even for non anime fans, extremely addictive story and... stick with subtitles, the dubbing will kill the whole thing. (And I actually liked the fansubs better than the official subs, they were a lot more detailed and had nice explanations for very interesting things).