Part of the reason I like Lucy is that when you say the word "Narnia," the first thing that comes to mind is the image of Lucy walking up to the lamp-post.
I feel like most of the story is told through her eyes. I understand what you mean when you say she's too "good." All I can say is normal rules don't seem to apply to these stories. That's what makes it a classic.
And, Georige Henley is the only person that could have played Lucy.
