I have never read any of her books but you talking about great characters and character development got me checking out goodreads. Characters are what make the story. When you get to know them and understand the decisions they are making, you feel for them, may it be awe, sympathy, remorse, or a simple friendship/bond. I know that feeling when you close a book and all you really want to do is cotinue the journey with the character.
RE: A storyline is key but it's the characters who bring it to life