Sadly, the people who should read this review will never even get past the words "Princess Tutu". I say that because despite the title, this video is not some cutesy, children's anime. Instead, this series is probably the best I've seen all year.
The series borrows heavily from many classic ballets, operas and fairy tales. Indeed, most of the soundtrack is Tchaikovsky and other composers, including my favorite song "Pictures at an Exhibition." And despite the cute, soft art style, there is a lot of darkness going on in this story, much more befitting of the soundtrack than the images.
The series is about a duck named Duck (Aihiru) who becomes a girl, who can then turn into "Princess Tutu", (her theme is, fittingly, from Swan Lake) a character from a story that suddenly begins coming to life. As Princess Tutu she can recover the "heart shards" of a boy in her school, who also winds up being the prince from this story.
There are a surprising number of twists and turns to the story, and just as you finally decide whose side everyone is on, things change again.
This movie also uses the idea of leitmotifs, overarching musical themes tied to each character, which then morph into the larger scores when dramatic moments occur, a concept created by Wagner.
And, speaking of Wagner, though I'm sure some will disagree, I found this movie had much the same epic feel as the Lord of the Rings movies.

To put it in numerical terms:
Art: 9/10. Gorgeous looking, the intros look like pictures right from a storybook. There were a couple of places I disliked the design of something, but for the most part, incredible.

Plot: 10/10. Borrowing from many of the best plays, dramas, and ballets of the past few centuries, it also manages to weave a story that is completely its own, with stories within stories.

Characters: 7/10. A couple of the characters were a little weak, and there were SO many supporting and one-shot characters.

Music: 10/10. Tchaikovsky, Mendelssohn, Bach, Mussorgsky, and more. If you don't like the soundtrack, you don't like music.

Overall: 9.5/10. Definitely the best series I've seen this year, and possibly for a number of years. Truly the only thing keeping this from a perfect 10 is my disappointment with the last, oh, 2 minutes of the series. But still, I recommend it to everyone out there.