TL;DR: Mildly entertaining and looks great, but with bad story and combat.
Without getting into the story too much, the foundation of the story itself is alright, although simplistic. The problem stems from how the foundation is built upon. In this case, the walls are as fragile as glass and the roof is made of paper. The backstories are as ambiguous and boring as they come, "I was an angel, then I was not, now I want revenge" (That's a made up backstory, not in the actual anime). Emotions are people saying "I love you, I envy you". When we see the 7 sins make
people fall for their lust, greed, gluttony, etc. It's absolutely not as demonic as you would imagine of "Demon Lords". What's worst is how there is also no world building. We don't know what these angels or demons are capable of, their differences in power or how their mana system works.
Art & Animation :
The character models are superb, environments are okay and animation doesn't have any faults. But the combat scenes are absolutely horrible.
They look good, but we know nothing about (most of) them. Their ideals? Backstories? Nope, we know nothing. Considering the small cast of characters, you would expect more than we get here. One of the main characters, Maria, is a complete doormat and her personality is being kind but dumb and pathetic. The most fleshed out characters are Levy and Lucifer, but even they aren't anything special.
Girls moan and nudity. Some episodes have an entertaining narrative.