The primary complaint people have about the main character (MC) is that he allegedly makes decisions based on his physical desires. It's important to note that he is only 16 years old and was a virgin until entering this new world. In a scene where he's at the royal palace, some got upset because he allowed a maid to attend to his needs despite her being naked and embarrassed. However, it's unrealistic to expect someone without prior experience, like a sage or someone who has been intimate with numerous women, to have such self-control.
The MC isn't portrayed as a pervert forcing himself on others; he waits for the girls to approach him willingly before engaging in intimate relations. Critics argue that he lacks motivation to become a hero, but there's already an established hero in the story. Moreover, he has already saved the world and faced political manipulation due to his power, which led to his involuntary return. This might explain why he's hesitant to embrace the role of a hero, fearing a similar tragic end.
The MC is incredibly overpowered (OP), but he tries to remain低调 to avoid attracting unwanted attention from ambitious nobles, royalty, and religious figures. Despite his efforts to keep a low profile, he doesn't tolerate being pushed around easily. For instance, when he encounters the demon kin (his second harem member), who challenges the hero, he easily defeats her after a duel in which the hero and his party are outmatched.
It's unfair to blame the MC for not being able to unravel complex schemes, given that his expertise lies in combat, as he was primarily focused on that during his time as a hero.