The people writing 1 star reviews simply don't grasp what an anime is compared to manga. They punish an adaptation because of the parallels they draw to it don't meet their expectations which is a hilariously small minded way of approaching an animated adaptation.
The anime itself stands on its own even with the way they portrayed the characters/art style and story pacing. It's arguably better than the manga in a lot of ways, but obviously falls short in others. That being said, the anime itself is incredibly binge worthy and does everything it needs to do in order to make you feel attached to the characters and invested in the story it tells.
Beyond that, the complaints about sexualizing aspects or pregnancies at a young age is not something that should be the sole reason an anime is rated so low. Pregnancies at a young age happen. That's reality. Regardless of cultures. Reincarnations from an old man to a young baby who happens to idolize the mother (idol) they were born into does not = sexualization. If anyone who complains about this bothers to actually take time to watch it and pay attention, you'd see that there is no sexualization. In fact the anime goes out of its way to emphasize the MC is against such aspects and it is very obviously shown pretty early on.
Watch it, draw your own conclusion, and remember this is just an anime adaptation. Manga d*** riders who can't articulate complicated view points/opinions should not be taken seriously.