Yeah there are many incest animes at the moment, some which was fine watching like Onii Chan and KissxSis,
Yosuga no Sora was... different, but could still be worse..
and then there are those which overall sucked (IMO)
Aki Sora
Aki Sora Yume no Naka
Boku wa Imouto ni Koi wo Suru (I love my younger sister) <--- was even worse than Aki Sora..
some other titles (haven't watched) goes all the way back to 2000-2003, so its not only in the newer times:
Koi Kaze
Candy Boy
Please Twins (Onegai Twins)
Angel Sanctuary
If its a fair amount of incest, then nothings wrong, but some are crossing the line..
Quote from "Papa to Kiss in the Dark"
Mira Munakata is a typical high school freshman; he goes to school, hangs out with friends, and has sex with his father.
i believe... that they went to far . . . yaoi.. ew...