This is going to be a short review because, despite the fact that I did actually like this series, there is not a lot to talk about because it is such a standard, almost stereotypical storyline.
Mai Tokiha and her brother Takumi are on their way to attend the prestigious Fuka Academy when their ferry is suddenly caught in the middle of a battle between two girls with apparently supernatural powers. This is only the beginning of Mai's troubles as she eventually discovers that she too has special powers -- the powers of a HiME.
The plot is relatively straightforward and focused, while at the same time it maintains a certain level of mystery. I'm not saying that the mysteries are especially gripping, but they did keep me curious enough to maintain my interest.
There is a lot of action in this show, but there is also a lot of focus on developing the characters' relationships. The HiMEs' powers comes from feelings they have for the "person most precious to them" so if a HiME looses a battle, that person disappears. As cheesy as that may sound, the show makes it work by keeping the melodrama relatively low key. There are also plenty of love triangles and awkward teenage romance. But it avoids getting too angst-ridden because most of the time the focus is on the characters trying to maintain their friendships instead of building conflict.
The characters -- as with most everything else -- were pretty standard with one exception: Makoto. In fact, a good portion of my enjoyment of the show is due to her character. Part of that is because she has such a cool way of fighting. Basically she spins her giant sword along the ground with sparks flying until she builds up enough inertia to swing it at her enemy... Just trust me, it looks cool. Her personality also made her fun to watch too. Most of the time she acted just like a cat, lazy and affectionate, but once you get her going she's one of the strongest HiME in the show, especially when her "dark" side comes out.
The animation and art are colorful and vibrant and are consistently above-average quality. The music works well with most scenes and does a good job of bringing out the drama in the action scenes, although much of it is recycled throughout the show.
Unfortunately the ending is disappointing. It seems rushed and doesn't explain many key points satisfactorily -- like (spoiler)
Overall though, I really did enjoy this show. It may be low on originality, but the story entertaining enough and the visuals are vibrant enough to make this worth picking up.