While on the surface this might be your typical action harem, there are several key differences that ultimately make for a more enjoyable series than expected.
Pretty standard demon girl-type story. Human comes across demon, somehow gets hitched with it, works to save the world, has ecchi and romantic encounters along the way. Plot twists are pretty obvious, lots of plot armor, etc. Overall, the story isn't anything to cheer about. The ending is also rushed to hell compared to the rest of the story.
Standard to sub-standard. Designs on main heroines are inconsistent at times. The girls are decent-looking, but short of pretty or sexy. Sometimes the art feels slightly incomplete for a main character. Best-looking/interesting character is actually a common antagonist grunt (the church soldiers).
Not the most memorable, and actually a rather stereotypical cast. Token sexy main heroine, token glasses sub-heroine. Token annoying frenemy duo. Even the main character is an unremarkable token latent-talent human for the most part.
What DOES set this series apart from others like it though is that characters have initiative, actually bother to think, and aren't morally black and white.
1. Initiative: The characters don't sit around and play silly mind games. When they resolve to do something, they seek out the necessary people and items and get it done, fast, rather than wait for shit to happen. It also helps that there aren't tons of filler chapters that makes you question the plot: "Wait, there's an impending demon attack and you're...at the beach?" (there is a beach chapter though, ha.)
2. Thought: The MC is the best example, especially during fight sequences. Rather than charging in blindly, substituting courage and plot armor for skill, the MC takes some time to plan his actions, and the author actually cares to show this.
Side characters do this too in the sense that they don't fret over small details, especially during ecchi "aftermaths." Sure, the offending MC will get his due punishment, but they understand what was an accident and what wasn't, and they know when NOT to bring down the hammer, e.g. while the enemy's right there. They also don't go over the top about it.
3. Grey Morality: This isn't one of those "let's defeat evil" kind of universe. If you like the idea of enemies becoming friends and vice versa, you'll feel right at home. There's no clear "bad guy," and a lot of characters are doing things for their own interest, whether good or bad.
All of these things said, I might be overthinking because I'm biased against typical action ecchi harems, but I found these points refreshing.
I enjoyed it. It was a fun read that never got frustrating thanks to the characters' sense of initiative. The story felt a bit rushed, the characters felt a little shallow, and the universe could have been expanded a lot more, and the ecchi scenes felt a little forced into the story, but not once did I feel like dropping the series or rushing to the ending. There are worse out there if you're looking for an action ecchi harem.