The show is set in a Japanese highschool and centres around a group of girls who all have a special ability called HiME. This ability allows them to materiealise weapons and avatars with which to fight monsters (and also each other).
The show has good characters, with some very interesting inter-personal reationships and character development throughout the series. Somehow though having seen the sequel (mai-Otome) the show just isn't as good as it could have been and lacks something to make it really special.
All in all though it is a good show with some good moments and i have to confess mai-otome is much more interesting if you have seen this show first (all thaough it is not essential as they are not really related).