I think it's just a signature move for his ouevre: I think he considers himself as an auteur of porn (see, I used two $20 words in one sentence). An interesting question to me is which directors and/or movies can be considered artistic works rather than just, ahem, porn?
To me, there are two qualities that elevate JAV; Plot and acting. Most JAV is pretty straightforward--like the SPRD series where the Mom is fucked by a number of her son's friends and he's forced to watch and/or join in. And there are a bunch of movies in that series, and sometimes the actress "sells" the situation better than another. But you know what's coming. I love that series.
AVOP-155 (which I have with English translation). however, is a really interesting movie where a guy is released from prison and winds up in a relationship with his long-abandoned daughter. It has suspense and sex, and a really unexpected ending. Highly recommended.
Many of the JAV derived from hentai are interesting in this fashion as well. AVOP-072 (good subs on this one too) is based on Cage of Hell, and has my favorite Yuko Shiraki and her two daughters overwhelmed by gangsters seeking reparations from the debt the father owed. Spoiler alert is that he his shot early in the film and then it gets interesting.
MEYD-449 stars Maka Oda and the plot is rather simple: Dad remarries a hottie and his son accidentally(?) witnesses her having sex with Dad. How will things progress? It works because of Maka's performance.
URE series has several movies that have interesting plots where it's not just the sex, it's the "what happens next"? How is this going to play out? URE-019, URE-30 are great examples.