This anime is another one of my favourites, it is currently fighting Black Butler and Ouran for first place in my heart (Angel Beats doesn't compete because its special). It's funny and light hearted, my only real issue with it would be the occasionally awkward sounding dialogue but then I am a difficult girl to please in that regard.
I love the story line and I think it develops well over the episodes as well as being easy to follow. The characters are interesting, particularly those with a demonic background and the animation is great. I love the voice actors on this one, especially Satan. I like the way the relationship between the brothers is betrayed as well as the way the interact with other characters. All in all a great show and definitley worth a watch!