Wow. This is just 84 pages of yay!
I don't know that I can add much to what every pony has already said, but here goes anyway.
What I probably love the most about Fluttershy:
Fluttershy is not a cliché. She has a personality full of such depth and beauty.
Fluttershy avoids fame and pride (Green Isn’t Your Color; Filli Vanilli). The spotlight (literally) is anathema to her. Even when she is doing something she absolutely loves, like singing; Fluttershy takes care of herself through her shyness.
She is such a sensitive pony that she is easily hurt (Hurricane Fluttershy; Griffon the Brush Off). Even a judgmental eye can feel painful to this gentle pony. To avoid hurt she hides from ponies. However, without this sensitivity she could not be as kind and as caring as she is. It is her sensitive heart full of empathy that gives her kindness authentic strength.
She may be fearful but can put this fear aside to help others if need be (Friendship is Magic; Dragonshy; Keep Calm and Flutter On). Because of this she can be suddenly brave in defense of her friends. Even then she avoids hurting other creatures if she can.
However, she can also be too kind and neglect herself (Putting Your Hoof Down; Trade Ya) or overly kind and enable others in a way that is not good (It’s Not Easy Being Breezies). But that is one of the things that is wonderful about her. Because she is genuinely kind and caring she inspires these qualities in other ponies. In the above examples, Rainbowdash remembered to be loyal and to care for Fluttershy, and Seabreeze learned by her example to be kinder to others. Even Iron Will learned something about kinder assertiveness, instead of his usual aggression, with the lesson of “No means no”.
Her ability to care and empathize is so strong that she will give other ponies a chance when her friends would not. It is because of her that the Manticore was “defeated” (Friendship is Magic) and that Discord is reformed (Keep Calm and Flutter On). It was also in Keep Calm and Flutter On that her shrewd intuitive intelligence was made most apparent. While other ponies’ may mistake her kindness for naïveté she clearly showed and stated that this is not the case.
In conclusion, Fluttershy is truly a wonderful pony! She is such soft kindness with a heart of incredible compassionate strength!
Yay