My otaku senses were tingling so badly the other day, I had no choice but to go and purchase the first 3 volumes of Sora no Otoshimono (chinese translated). Like the anime, the first few chapters are light-hearted, filled with comedy and fanservice, but...
the storyline can get dark at times, especially when the past of both Nymph and Ikaros get brought up. We get to see Nymph being abused by her actual angel master, forcing her to kill her friend/pet, making me feel kinda sick.
However, looking at Suu Minazuki's past works, I guess the above is to be expected, since they are always dark in some sense.
I hope the anime remains in the comedy and ecchi-fanservice genre.