I am going to say first off that I am biased because I am a guy and this show is borderline hentai at times.
I would have to say that I liked this show so much because of Issei. Not only is the character funny as hell, but voiced by a superb actor. There were scenes that I thought were incredibly stupid, but then I would hear the Issei voice of conviction and become psyched. The goosebumps produced from his determination was frequent... Not just a 1 episode thing.
On another note all of the girls are super sexy and drawn with perfection. All of the characters are unique in some ways and make the show very funny.
The story is a bit iffy from time to time, but I'd still like to see where it leads... This is definitely more for the laughs and the half naked succubi though.
If you like succubi i'd say you just found your next show to watch.