Idk why people in this comments thread hate this manga, but it's just your regular isekai nonetheless? It's just this manga has a male mc that's resembling NPC rather than courageous protagonist you usually find on isekai manga.
He's a laidback person, the slimes are very cute and supportive, and the other characters are not dragging him to stay and help them forever (which is nice imo).
If you asking about plot, there's a plot going on albeit in slow pace. If you're looking for a fast pace manga then this is not exactly for you. But if you just want to read something isekai then you can read this. I guarantee you'll hook up with the story once you read it.