I'll cover both versions of the anime; the original Japanese and the English dub, reviewing the storyline/direction for the Japanese version as well as the main voices, and the voices for the English version. NOTE: this is not about the original manga.
The quality of the anime is pretty good overall. The art matches Toboso's well, and they include a lot of the details that are part of Ciel's extravagant outfits.
The creepy factor, I think, was amped up quite a bit, which might urk some people, but of course, I don't mind it at all. As for the music? It's positively wonderful. It fits with the series, and the...well, I can't quite describe music with words. You'll just have to listen. I especially like the opening theme 'Monochrome Kiss' and that sad background piece, 'Si Dues Me Relinquit.'
Daisuke Ono really nails Sebastian with the smooth, flowing, mysterious quality that he adds to his voice. He actually does a decent job with the English pronunciation of 'Yes, my Lord.' Even though Sebasu-chan is a demon and is not supposed to be expressive, Daisuke adds emotion to him that makes him even more likeable, as if that were possible ^^ Ciel:
Oh, wow. Maaya Sakamoto is truly amazing at her role. I know I said I would try to be impartial, but there's just no way I can when I'm talking about how accurately and wonderful she plays Ciel. The emotions and tone of voice she conveys are pitch-perfect. You can totally see Ciel's personality shining through just his voice; you don't even have to watch the animation. If you didn't know, she's also the voice of Haruhi Fujioka from Ouran High School Host Club. Grelle:
If someone can play a bi-sexual reaper, it's Jun Fukuyama. His voice is a little...raspy (?) and crazy, and, well, perfect. You could tell he was having fun doing it, and wasn't holding back in the slighest. If you ever watch him doing some live fan stuff for Kuroshitsuji on YouTube, you'll see what I mean. Undertaker:
Oops, I'm afraid I don't know who plays the Undertaker. Anyway, whoever he is, his laugh and creepy 'sends-chills-up-your-spine-everytime-he-makes-a-sound' type of voice is awesome. Soma Asman Kadar:
Since Soma is really energetic and...emotional, I think Shinnosuke Tachibana really nailed him. His voice isn't too deep or too high; it's perfect for the character and Soma's age . Agni:
Agni's personality is portrayed perfectly, and the voice ranges from serious and comedic moments are smooth. Hiroki Yasumoto's (Germany, Yagari-sensei) deep voice is awesome for his character, even though he [Agni] is a bit eccentric.
For time's sake, I won't list out every character's voice, but overall, each was at least decent. They put some good work into it.
It seems that a lot of people are unhappy with how the long-awaited Dub came out. Read on to see what I have to say about it.
As our favorite demonic butler, we've got J. Michael Tatum doing our voice. I'm pretty new to the world of dubbing and such, but with a little research, I found out that he usually gets cast as the more eccentric characters; France (Hetalia) 'Doctor' (Black Cat), etc. And Sebastian is a rather eccentric character, so it's really no surprise, is it? I was pretty surprised at the direction it was taken at first, though. For one thing, it's sure as hell a lot deeper than Daisuke's, and doesn't have that 'soothing' quality. The English Bassy (no pun intended) is very business-like and serious, and the sarcasm/jokes come out a lot more...devilish. His chuckle is rather ingenious, though, I must say. I think that Toboso portrays him as a slightly older man than Daisuke makes him sound, so in a way, Tatum gets a little closer. Ciel:
Hmm... Brina Palencia seems to be the source of a lot of fans' hate at the moment. I, like many others, think she could have done better. She's trying a bit too hard to make her voice sound like a young British boy, and you can easily see it. But it doesn't necessarily destract from the dialogue, which helps. The only real issue I have is that her 'Ss' are a bit slurred... Grelle:
Even though I love Grelle as much as I do, Daniel Frederick didn't do as good a job as he could've. But it still was a pretty good 'performance' for a newbie to the world of voice-acting. His voice seemed a little quiet, but maybe that was just my speakers... Lau, Madame Red, May-Rin, Bard, and Finny:
Jerry Jewell, Lydia Mackay, Monica Rial, Ian Sinclair, and Jason Libreict were excellent at their roles, however small they may be. Sinclair and Rial sound like the exact American versions of the Japanese seiyuus. Libreict was a little over-the-top, but I think it turned out okay in the end.