So what did people think of this? To me, it smacked of Donna Troy syndrome: let's give an established superhero a completely different backstory, which changes his tone, his personality, his place of origin... (And J'onn's had a bunch of those already.) It feels like it's out of continuity, but I'm not even sure what that means these days.
It also had an unexpected level of what some people might consider "adult content." "...I hope you're penetrated by H'Ronmeer's Holy Hot Fist!" Maybe that's a pious religious reference among Martians, but it's not what it sounds like.
It's hard for me not to react to this issue by saying, "Why do this to J'onn J'onzz, specifically?" Maybe I would have liked it more if it were about some new character, not part of the DCU.