Gonna break this up into categories.

Characters: Every girl has their own personality and look. That sounds like faint praise but in a porn game that's top of the list for me. Seeing characters bounce off each other and the dynamics that arise from new situations is important. And that's something Eternum absolutely nails.

Plot: Urban Fantasy meets Sword Art Online. Which should be terrible because Sword Art Online was terrible. But Eternum manages weave the "real" world into the "videogame" so well that as a reader, I ended up with no real preference for where the story went. The classroom stuff was just as engaging as running from a burly monster.

The interjection of logic into the setting was also very well done. Eternum convinces you of its conceit (a hyper realistic virtual reality) and then asks you to question it (how exactly is a lag free, glitch free hyper realistic virtual reality possible) at just the right time. And it doesn't come off as a surprise because it doesn't take long to notice something is wrong with Eternum.

Humor: Somewhere at the intersection Archer, Porkies, and Bromwell High. It is... not what I usually go for. Thankfully everyone commits to the bits so hard the comedy just works. In fact timing might be Eternum's strongest feature. Whether it's going for a joke or for a scare or even for a sudden reveal, Eternum always holds the beat just long enough for the desired emotion to land.

Misc: If the rise of filmmakers like Jordan Peele and actors like Joe Pesci have taught me anything, it's that comedians deserve way more respect. Caribdis really manages to nail whatever emotion he's going for. The horror sequences are genuinely anxiety inducing. The romantic scenes actually make me want to see the characters cuddle. They've done a fantastic job.

Final: This is a harem game so if it's not your thing I can understand avoiding it. But it is a very well made visual novel. And if the premise isn't a deal breaker I'd encourage everyone to give it a try.