I finished watching "Mai-HiME" a couple of weeks ago. On the whole, I liked it, though it took a long time to get really good.
It was recommended by friends whose taste I trust, and I'd rate it as a solid B+.
What starts out as a fairly standard "magical girl" shoujo series turns surprisingly dark around episode 15 or, and the writers use all the sweetness-and-light from the earlier episodes to crank the jeopardies really REALLY high while paying off some of the setups from earlier episodes.
For the first 14 or so episodes, it's a well-done but rather standard "schoolgirls with superpowers band together to fight demons and a big evil conspiracy by the grownups."
There's an interesting split in the mood and style between eps 1-14 and 15-26, almost as if the original writing staff was replaced by writers heavily influenced by Joss Whedon. The storyline turns very very dark, very angsty, and the jeopardies are cranked sky-high.
Bad Things begin to happen to Good People, and the atmosphere of friendship and cameraderie amongst our group of super-schoolgirls starts to distintegrate in some very ugly ways. At this point, I was hooked (and stayed up until 2am several nights in a row to watch), and the stakes remained very very high despite a few repetitive story beats.
I wasn't convinced by the end...I felt it was insufficiently set up. When the conflict finally wraps up, there's a happy ending that feels rushed and sort of comes out of nowhere, considering the deep emotional and physical wounds sustained by our intrepid cast.
After all of that lust, jealousy, unrequited love, murder, betrayal, suddenly everyone is friends again. Um, I think not, but it wasn't enough to ruin the series.

buh the manga is worth more...

