A mythology-based hentai, Angelium (at least slightly): It's about how 3 angel apprentices undergo the "angel's test" in order to become full-fledged angels while having Zeus, their god and leader, present them sexual obstacles in the way. However, there's a hidden motif for Zeus's harsh training... But you'll have to find that out by yourself; I'm not spoiling it. The mythological part I mentioned is that they base the characters in the Greek mythology: Zeus is married to his sister, Hera, but still has multiple relationships with other women, out of marriage. Hades is the god of the underworld, with his queen Persephone, and wants to gainmore power.

Art and animation is alright, the depiction of the female body is fun to watch (in any way you want to think of it), although it could've had more details and better shading techniques.

Sound is just fine, it doesn't excell in anything, neither in a bad way nor a good one.

Character development is very superficial. The main characters are left unexplained basically, and the secondary characters, you will only understand them if you have read about Greek mythology in the past.

Overall, the series is alright if you like hentai animes and sexual scenes. If hentai is not within your likings, don't bother.

P.S.: For the producers, just because it's a hentai, it doesn't mean you don't have to come up with interesting stories! Come on, gives us hentai series with good, well-developed plots!