By 2005, the hentai-with-a-story genre was pretty much dead already. You'll only find mindless porn scenes, just intended for self-pleasure. Hininden is a surprising exception to this fact, although it obviously contains sex scenes too, along with funny scenes and above average character designs. It is great to see some production value destined to improving animation and graphics quality, but apparently this lead to Pink Pineapple having financial trouble, since it didn't sell well. As expected, this single episode pilot was sadly canceled and unfinished, like many other hentais in the past. Before this OVA, 75% of Studio Arms catalogue also consisted of hentai-with-a-story animes,so they definitely had experience in this genre.
In conclusion, Hininden is an interesting, entertaining, short-lived chapter of a dead genre. Not exactly a hidden gem, but it is a bit sad that it didn't have a recommended review until this one.