About Mushoku Tensei, the differentiating factor is that there is some visibly higher degree of effort involved in making it. The difference in art and animation quality is immediately noticeable (they take no "shortcuts" unlike all others), not to mention its deep world-building and how it treats none of its characters as black-or-white. At its core it is still just an above average isekai, but more importantly it's a high-effort endeavor throughout.

... it still could do without constantly bringing up sexual degeneracy though