Yajin Tensei is a little like what you would expect an isekai with functioning humans to be like. An average guy who learnt some karate is transported to another world, shenanigans ensue. Two things though, make this piece stand out to me as something more than just your average isekai manga. For one, it's heavily subversive, and comedically self-aware about it. Don't expect waifus or harem's here. The world more than anything else resembles the kind of gritty darkness of Berserk(though it never goes full on dark) than it does arifureta or shield hero.

More importantly, the author understands the genre he's writing for extremely well. Yajin Tensei is an adventure story, first and foremost. It's a picaresque novel in the vein of Tintin or Raiders of the Lost Ark. It appeals to the exact same sentiment as One Piece would. It's not a work of great depth, though there are occasional moral ponderings by our main character. It's an extremely fun story to follow along, and it handles the subject matter well. And in a sense I have little else to ask of an adventure novel than that. Would I reccomend it? Absolutely, one of the best written works of genre fiction out there.