It's fairly cool to look down on this series, and it really is a study in strengths and weaknesses. However it is the sort of series that once started you really want to know how it ends. The story centers around a magical book that acts as a portal to another world. The book promises that any who enter the world, and perform certain acts, will be given the power of a god. Two young girls, Miaka and Yui are attracted to this book and forget the important point of magical contracts, read the fine print very carefully, as the truth is nowhere near as simple as it seems. Neither is the story, for in fact there are four gods tied to four kingdoms, none of which want to be the one without a god on their side. As possible priestesses of a god the girls hold immense potential, which of course immediately involves them in politics, sinister manipulations and great danger. This is especially true because while the girls have great potential, they have no special powers until that time. To balance this there are seven `seishi', chosen warriors of the god, who will protect the priestess, although they are hidden amongst the people of each kingdom, albeit bearing magical symbols which grant them different magical powers.
In total there is a very large cast of characters, and some of them are very cool and complete characters, while some are largely left in the background. This really annoys those who have read the manga, but its fairly unavoidable given the size of the cast. In addition we spend a lot of time getting to know Miaka, who many people find an irritant. I consider Miaka a wonderful study, she is not overly bright, is impulsive and acts rashly and takes things to heart with little restraint (especially the romantic interest Tamahome). On the other hand she is capable of amazing acts of empathy, self-sacrifice and bravery. She is the `lamb' character, when many would have preferred someone more capable in the lead role. And don't think this story is just characters wandering around talking, these characters are put in a blender set on pulverize. There is death (of main characters and in general), evil, betrayal, hatred, cold-blooded murder of innocents and rape in this world.
This world has it's periods of darkness, and there is a real feeling that no one is totally safe. Balancing this there is romance, humor (a lot of humor) and underlying it all the epic quest to tie it all together. This combination of epic fantasy, a shoujo interest in character and a lot of tragedy and humor makes an very rich whole. This is also where the problem comes in, the press of events is so great, and the writing of variable quality, that it does feel like the story jumps around a lot. Characters are sometimes required to do illogical things to allow the story to continue, some scenes are perhaps too sudden to be truly believable and in some scenes the balance of the story elements conflicts which can be quite jarring. Indeed many will find the authors preference for humor, even in the midst of tragedy, quite painful and cheapening of the whole experience.
This uneven quality also extends to the animation, which is acceptable but has lots of visual humor and occassionally seems quite sparse. The music is energetic but very nice, and the opening track is very good at setting the mood. While the production, and writing, does have flaws there is a lot to like about this anime with a rich story, deep fantasy, likeable characters and a clever conclusion. Of course those with an aversion to shoujo will probably find this a much more rocky ride.
There's a good review from the Anime Critic who likes it, but warns that it fairly shoujo, that it has a cool villain (very true) and that the endless Miaka-Tamahome relationship crisis are a bit much spread over 52 episodes. THEM seem to feel the hype is in need of debunking, and prefer the manga, in a possibly unfairly brutal review. There's a long, detailed and deep review from Akemi's AnimeWorld which makes a lot of good points.