So many people talk about the fault within two-dimensional characters. To a degree, I've always been guilty of this myself. However, I ask you to view them with a different perspective. If you were a character in a story, would your actions really appear to be any less two-dimensional? At this point, you might be saying to yourself, "But my life ISN'T a story! It isn't meant to be epic and original. It isn't meant to be interesting enough to tell." The story however does not necessarily relate to a character's outward expression... Or in this case, your outward expression. If another individual were to view your life and hear your thoughts for one period of your life, would that mean that they really knew you?
In order to really know a character, you have to spend time conversing and interacting with them. You have to analyze their reactions, as well as their actions. Bella from Twilight may have been a wonderful, fascinating person, if you knew her. Her life at the point she was expressed perhaps did not show the best of her.
When it comes down to it, only a writer really knows their character and their deepest depths. There are of course writers that under-develop their characters, but whether or not there was actual under-development or they were merely under-expressed, you will never know.
And I'm not saying that you shouldn't judge a piece of literature for what you see it as. As a person, it is your right to judge. I merely ask you to acknowledge that if you could converse with that character with all of the heart and creation put into them that you never saw, you might be able to come away with a very different perspective on who they are.

But I'm just rambling and this was a surface thought I had. Perhaps I overlooked something. I typed this as it came to me. So, if you have any rebuttals or thoughts, I'd like to hear them.