I HIGHLY recommend Bible Black, its one of the best H-anime i've seen up to date.
Its funny, has a scifi plot, and only one scene that has tentacle rape but even if u dont like it, the situation in which it occurs will change ur mind
Most hentai have crap or ludacris stories, but this one's is actually on a very good anime standard. I personally love it and wish they make a none-H series of it, continuing the story.
What might put you off is that it DOES have a transexual, which is the villian, but the graphic quality, animation, stoy, comedy and sex make up for it. 6 episodes with a 5 episode sequel, and 4 episode extras. Look for a torrent :D