I can safely say that this is one of the more origianl series that I've had the fortune of seeing. Edgy, dark, and tantilizingly mysterious this series will grip your mind and emotions and squeeze them violently before letting them go. That being said, this is definetly more of an "accquired tase."
~Story~
The plot synposis does not in the least do this anime justice. I get the impression that most people who just look at the plot summary provided here will perceive the anime as being something radically different from what it actually is, not to mention it really over-simplifies matters. Let me say that the intricate story really drives the anime. You don't really know exactly what's going on until the very end, which keeps things exciting but can also be very aggravating. The plot, backstory, and characters themselves are all revealed bit by bit rather than all at once. Certain aspects are given in a straight-forward fashion such as Kazmatsuri's backstory but most everything dealing directly with the main conflict is shrouded in mystery. The show's tagline: "Whose side are you on?" is rather befuddling in that you don't have any concept of the true motivations and natures of the two warring sides until the very end of the anime. While everything seems to boil down to the explosive and twist filled ending, this anime is not one that I found to be end-enduring; in other words, you didn't keep watching solely due to the anticipation of some profound conclusion like you do when watching Witch Hunter Robin. The anime itself was entertaining and each episode self-sustaining.
A word of caution: this anime is extremely saturated with symbolism. As such, those with analytical perferences may enjoy it more than those who don't like to delve too deeply into metaphors or philosophy. However, the anime is still rewarding for the latter category...until the end that is. The ending is very in your face symbolic/deeper meaning, and if you're not willing to try and puzzle out what certain things mean in the grand scheme of things, you will feel cheated. I myself initially thought the ending was a total creative cop-out the first time I saw it. After spending hours scouring fan forums, reading the interpretations of fellow fans, and also reading essays on the Epic of Gilgamesh on which the show derives its name and borrows some narrative and thematical elements, I now greatly respect and appreciate the ending. So, if you are unwilling to read up on the Epic of Gilgamesh and discuss the ins and outs of the metaphors snuggled in the ending, I'd warn you to bypass this anime or else risk great disappointment.
~Art~
The art style was what originally drew me to the series because its so different from anything currently out there. I will admit that it takes some getting used to. The majority of the production is filled with dark, cool color schemes and shies away from pastels and vibrant colors with the excpetion of the color red, which is used liberally to emphasis emotion, passion, violence, and character associations. The character designs are all very distinctive, strong, and unique. They too take some getting used to what with the clumped, sharp looking hair, deep, penetrating eyes, and large lips. The one character who looks incredibly and immediately awesome in the given style is that of The Countess. I am of the opinion that the entire style was implemented just for her character.
My one beef with the art of the show is that some of the action sequences are a bit sketchy. It almost seems like certain enouncters are more implied rather than shown, which can be irritating. The degree to which the action sequences are developed fluctuates greatly with some being gorgeously choreographed and others seeming hasty and incomplete.
~Sound~
From sound effects, to background noises, to in episode music, this anime excels in its ability to sate musical desire. The only bit of music in the series that I would not call high caliber would be the ending theme. My roomie and I had a good laugh at the long standing joke that I could sing just as well as the ending theme singer, and let me just make this painfully clear: I can't sing. At all. It's akin to hearing a cat get run over at high speeds on a mile trek of broken glass. That being said, the ending theme did grow on me. Wether this was due to the immense pleasure I got out of caterwalling along with it each time it played or due to a genuine enjoyment of it, I can't really say. In any event, I recommend joyfully belting out the ending theme each time you get to it for all your neighbors to "enjoy."
~Character~
I don't really feel like commenting much on this one. I will tell you that I liked each and every character in the series. Especially Kazmatsuri. At first glance, he's a cold-hearted jerkface. But after you get to know him...he's cold-hearted jerkface. The main reason I love him is specifically for one scene towards the end of the anime. I won't tell you what happens, but look for the episode in which the kids go demand answers from him at his home. My roomie and I about died laughing because of something he does after they leave ( I suppose the humor or lack there of is purely subjective, though, but at least his action is unexpected). Look for it!
All in all, this is a delightfully wonderful series. Not for the faint of heart or young of age, mind you. It does get a wee bit violent and generally deals with things in a more mature manner. (It's nowehere near Akira, Elfen Lied, or Hellsing standards though. Meh. I'm venturing it'd be in the PG-13ish range...ish. Some scenes are gorey.). It's not for lovers of things light and fluffy although it does have some preciously fluff filled moments. But, if you're in for something original and you've got a desire to go all english essay and analysis happy, I'd say go and get this. Now! DO IT NOW!