The music is the greatest part about this hentai. While it is not exactly stellar, its usage brings a very powerful sense of suspense and mystery. It's enough to bring those butterflies to your stomach, which is the reaction to a large threshold of a thrilling experience. The ability for the use of music, and the absence of it, to permeate the entire series with this feeling is an incredible feat. However, where this hentai falls short is in its main purpose, to be a fap session.
The art is low quality, partly due to it being an old hentai, largely due to it lacking in sexiness. In terms of a hentai, it's sex scenes are very toned down. The music builds up a very powerful emotion, but the actual scenes are too weak to live up to the expectations of the buildup.
The characters development is cockblocked just as much as the subpar sexiness is a cockblock. Detective Hiromasa Miyamoto wants to understand Seimei Abe, but Seimei doesn't give him any opportunity to understand anything by doing bizarre things. While this is fine for a mystery anime, it's pretty annoying for a hentai. Seimei is completely unrelatable and a nuisance. Her attitude is that of a haughty queen who does whatever she wants with little to no explanation. It's not cute nor sexy like a himedere, it's just annoying/frustrating.
If Onmyouji: Youen Emaki completely dropped the hentai scenes and just made the series ecchi at most, this would actually be a fairly nice anime series for an old anime. It already has an interesting premise mixing detective mysteries and divine summoning. There is also a cast of potentially interesting characters that are not developed due to how short the hentai is.
Onmyouji: Youen Emaki would ironically be sexier this way, as it leaves more to the imagination--which is valuable in any kind of mystery story. Unfortunately, it does not take this route and the sex scenes end up feeling awkward.
