Can't speak for the LN it's based on, this could just be a bad adaptation, or at least a truncated one that just ends with no resolution. But as the review states, it had a good start - some legitimately hilarious scenes. I also like the characters for the most part.
The issue is that once we get past the initial start and the opening scenes... the plot is terrible. For an 'Overpowered' Hero that not only defeated the Demon Lord, but then THE DEMON GOD BEHIND HIM, he's remarkably weak. Well, not, that's not really it, it's that he uses 'clever' solutions to winning, instead of... you know... just winning? Next he'll be bringing guns over to a fantasy world, because... reasons.... even though he's a Hero. Like he brings out a chainsaw to cut logs (?), and creates a wire trap to unseat Cavalry... like no one has ever thought of trapping cavalry before? Then instead of using the giant ass god-level dragon waifu to wipe out the army en-masse... he has the catgirl drop molotov cocktails from the same dragon to wipe out the army en-masse...?
WHY. JUST WHY?
And all throughout the story, the MC is a pretty empathic character (meaning him to his enemies, not the reader to him), so he feels guilt about getting involved in a human vs human fight, and so on. In the manga it's just BAD, but i honestly believe that it would probably be better in the light novel. On paper, having a MC have feelings is a good thing, but the WAY it was done in the adaptation was just bad.
Or the light novel was equally as bad lol, who really knows.
TL;DR: Maybe read the first 5-8 chapters? There are some good moments. Ditch the rest, it's terrible, and there's no conclusion btw. Just ends with his pseudo-harem apparently moving in with him on Earth, after a few page flashback where it turns out he can just take his mom over there and explain the situation and give her a tour.