We all know there is far too many Isekai stories out there. And this one honestly isn't a hidden gem or anything like that. But it is quite good, and here is way.
This author is really good at writing the story so it's easy understand, and still have a certain depth to the text. Battles are easy to follow and is very well explained. This makes the books relaxing while being very entertaining.
Good Characters: They all have fairly realistic personalities and is not too weird or overly dramatic in any way. The Main Character is pervert, but also too kind to make the
girls uncomfortable. While the Main Heroine is a very kind woman whom can become quite terrifying when she's angry. I can't find anything really annoying about anyone so far.
Good Art: The art is perfect for the "feeling" of the writing, it's simply a perfect fit and I have no complaints. But like many light novels, the text can vary a bit from the picture shown. While the character designs is fairly normal, the ecchi art is outstanding.
Mediocre Story: The story is fairly standard, but the author's writing skill makes it entertaining to read anyway. There is no real good or evil. When learning about the history of the world it's very hard feel sorry for any specific race. After 4 volumes, I can't see any real advancement involving the Demon Lord. There is much more focus on the world itself than the (supposedly) revived evil king of Demons.
Overall: It's very entertaining if you overlook the whole "summoned to slay the demon lord" thing and think of it as an adventure story where the main character is simply exploring the world.