I am unsatisfied wtih this ending, especially since it gave me better expectations than I initially had for something very "smut-based", I wanted to see more of the why the world was like that and how it would be fixed.
In a way is a good ending because that world is fixed and I guess he got to bring some powers into his old world, so I don't regret reading it and probably still would knowing how it ends.
This sort of setup always creates a sort of "debt", you have to pay it, to give a satisfying ending.
Wishing good luck to the author's next work...hopefully his art style changes, or he works on something where it fits more, because its characters looked a bit goofy, since they were supposed to be adults and they have the features of babies (fat faces, big eyes, chubby bodies).
I have seen way worse endings, from longer, more serious manga too.