I bought this purely on impulse when it appeared in my reconmendations, and now I'm glad I did. As soon as I finished watching it (over the course of two nights because it was so good I couldn't stop watching) I immediately went and bought both the manga and the second half of the series with next day delivery (something I never do because I'm a chepa-skate) as I simply couldn't wait to find out what happened next. The plot is both humorous and full of suspence, while the characters are so likable you care for their welfare for one reason or another, and the dub is among the best I've ever heard. I bow down to funimation for their expert pick of actors for this one!
If you like Vampire Knight, Pandora Hearts, or anything of that sort then this is definitely one for you. Even my friends, who don't normally watch anime, enjoyed the episode I showed them. It was an instant hit and I can't wait for the second series.
(However, I would recomend buying the series as one complete boxset, as it works out cheaper ;))