Well I can't promise you anything since I know you are a big fan of Nana. I don't remember why I stop reading it but the story didn't interest me that much after a while. I'm Not An Angel is quite a classic shoujo so don't expect big surprise but a nice story. From what I understood Gokinjo and Paradise Kiss reused some of I'm Not An Angel characters with more a fashion theme that is absent in the prequel. Since they are short, I will probably read them in a near future.