My main critique of the genre is how lazy it's done. There's nothing wrong with having the MC reincarnated, transported, or made overpowered. One Punch Man has a massively overpowered MC but it's still really good. The problem is that they're all low effort cookie cutter stories that are just checking items off a list.

They're also fairly unrealistic. "Gasp...is this that isekai thing I've been reading about? I guess I'll go join the Adventurer Guild and get a super dangerous job killing monsters despite the fact that I've never been in a dangerous situation before."

There's no way all these random people will just calmly accept finding themselves in another world with no freaking out or depression setting in first.