4.0

I think this is going to sound controversial to a lot of people but: the "As told by Christian Grey" books in the Fifty Shades trilogy are actually my favourite out of the whole thing.

Grey gives you insight in the mental struggles Christian goes through to cope with his feelings towards Anastasia Steele. He keeps telling himself he isn't the hearts and flowers kind of guy but all his romantic experiences in his life have all been with Ana.
You'll discover a lot of character development from Christian's side. He has been through a lot (abuse and assault) and that still haunts him to this day. And that kind of leads to him being who he is.

In the end he realises he can't let Ana slip away and is going to try to win her back. And he realises he's not the monster he wants people to believe he is.