I, like 99.99% of the people who watched this show, watched it because Sebastian is pretty damn hot. Luckily, this show is more than just a bishie-fest... kind of.
Story: Phantomhive Ciel, a child who just so happens to be the owner of a toy company, lives an extravagant life in Victorian England. He has a household of servants, most of whom cannot do anything servant-like. However, there is that "one hell of a butler"-butler, Michaelis Sebastian. Turns out, Ciel's parents died in a fire, so Ciel made a pact with Satan and now Sebastian serves him. Or something like that. However, each arc is different, so this story is more of a background, less of a plot. So I cannot bring myself to call the story "well-executed."
Animation: "Kuroshitsuji" (A.K.A "Black Butler") is known for its eye candy. Sebastian is gorgeous, of course, and his master is cute. (Don't kill me, Ciel-chan.) Character designs are pretty and very "anime-like," and the backgrounds and color palate sets the mood. Some scenes are wonderfully animated, others are completely average. Basically, it is great art but fluctuating animation. Nothing too out of the ordinary.
Sound: The various OP and ED themes are nice, catchy tunes (some fit the tone better than others, though...). Voice acting is pretty wonderful. Sebastian's seiyuu, Ono Daisuke (the guy no one knows SARCASM ALERT), gives a sexy voice perfectly fitting to the character. Grell's seiyuu, Fukuyama Jun (wow! What is with these unknown people SARCASM ALERT SARCASM ALERT SARCASM ALERT), does a FABULOUS job. He deserves an Oscar nomination. Everyone else is fine. And, as you may know, I tend to like English voice acting. While not nearly as good as the Japanese, "Kuroshitsuji" has a good cast, except for Meyrin's (sp?) ear-grating voice. And I usually like Monica Rial's work, too! Oh, and one other reason to watch this in Japanese... in one particular scene, Funimation subtitles Grell's words as simply, "WTF?!" Really. I practically died laughing.
Characters: Uh... let's see...
Phantomhive Ciel: Really, a love-him-or-hate-him kind of character. At times, he's a bit of a douche to others. Other times, he is truly kind to those same people. I like him, though. He never gets much development, though.
Michaelis Sebastian: He's more than just "Hot DAY-UM!" He's actually a badass "Hot DAY-UM!" He's actually not much in the personality department, but he can kill you with a butter knife and make fangirls swoon while doing so. That alone earns him some points.
Sutcliffe Grell: Yet another character who has a shot at being one of my claimed characters. Actually, I think I'll let this picture do the talking:
Really. (And disregard the spelling error.) The flamboyant, guy-loving, transvestite, insane killer is so likable, it's criminal. Every moment he has on the screen is yaoi-flavored comic gold. Worship him.
Undertaker: He's creepy, unsettling, disturbing, and just all-around awesome. Love him with all your heart.
Lau: I'm aware he's more of a minor character, but since I seem to be mentioning all the cool characters, I feel is should talk about him. His closed eyes may make you think, "OMFG it's Brock!", but the fact that he always has Ranmao (wearing a tight Chinese dress with a miniskirt) with him, does not invoke the "forever alone" feel of Brock from "Pokemon." Plus, the guy deals drugs. Need I say more?
It pains me to say it, but I have to knock down some points due to lack of development and some boring/or annoying characters. Forgive me, Grell-sama.
Overall: I'd recommend this to any yaoi fangirl or bishie worshipper, but to guys? Watch the episodes with Grell, Undertaker, and Lau. And do not even wonder who Elizabeth might be.