J Micheal Tatum has a British accent. That alone makes this anime one of my favourites. However, if I were to look at other factors I would say that the witty humour, the bad ass epilgoues and general kickass nature of Sebastian the demon also helped.
My only issue with this anime would be that it is slightly unclear near the end as to the background of Ciel and that sometimes Sebastian deals with things with a little too much ease. I'm not saying I want to see him bleeding in pieces (although that did nearly happen once) but a little bit more of a struggle on his part would be nice. Especially when he is dealing with demon dogs. But then we did see him break a sweat when fighting a frisky red head (Grell. Just, watch it for Grell.) and we saw him tied up, bloody, so I'm not too irritated by his invincibility.
Another thing I love about this show is it OVAs particularly the Behind the Scenes. If you do watch this anime watch that OVA it is hilarious.
All in all it is a great anime with plenty of punch and with dark themes. Not one to watch if you are looking for something light but definitley one you should checkout. It's fantastic.