The main issue with Eternum is that it feels like its creator is contractually obligated to add “adult content” once in a while, but couldn’t care less about it otherwise.
I mean, you’ve got this expansive universe, tons of events and dialogue… and the most vanilla sex scenes (although “foreplay scenes” would often be a more accurate description) seemingly as an afterthought.
The fact that the girls all have the samey “Illusion” look doesn’t help either. Once in a Lifetime wasn't exactly photorealistic, but its stylized art style made it work. Ironically, Eternum’s higher production quality makes its character models look jarring in comparison.
As for the story, it’s certainly told well enough, but relies too heavily on recycled elements from popular franchises and memes. Once in a Lifetime had the decency to not overstay its welcome, whereas Eternum might be too ambitious for its own good.
All in all, it’s not terrible or anything, and Caribdis has obviously spent a lot of time on this already so I’m not going to rate it any lower, but I wouldn’t necessarily recommend it.