I kind of feel like they're doing too many gimmicks here. Dungeons in Japan, unbalanced gender ratio, returning from defeating the demon lord. Pick one.
The art is quite good, but the story... I'm not even sure this can be called wish fulfillment, because what is even happening half the time? If the hero was so cartoonishly evil the entire time, you'd think ONE person might catch on, but apparently no???
BRO IS AN ADULT AND IS TYPING IN ALL CAPS COMPLAINING ABOUT FICTIONAL MEN ON A FORUM ABOUT MANGA. Let 'em live a little. It wouldn't be an interesting story if every character was 100% perfect right off the bat.