Number one thing that makes me drop an Isekai is that tose people (kids/teens) who get summoned just accepts that they are summoned to be sent off to war, and they just laugh. Like okay imma fight like in those games and might die. SO FUN!
Second is to simply use game mechanics as an excuse for magic in this new world. (Skills, Levelup, Item storage, a fucking HUD and appraisal. ALWAYS APPRAISAL.)