I'm currently in Day 1 (of 2 available), so this positive review may be pre-emptive, but I wanted to get my thoughts more concisely entered.
First off, I'd describe the game as "rudimentary", but not necessarily in a negative sense: it bleeds into writing, modelling, story, lighting, the whole shebang.
Models look almost porcelain, but vary in quality from the better-looking Aiko to the borderline ridiculous protagonist (who looks like the face of a 10-year-old was pasted on to a 30-year-old's body).* Rooms are described as 'full' with 5 people in a room containing 40 desks. I'm meant to be 30, right? Then why does my mother look 30, who I'm living with for some reason? I'm working at a high school, but* the default age is 20?? At least if you said the MC was teaching Year 13 (a real year in some countries) you could say they're 18 or 19, but I have NEVER heard of a high school with 20-year-olds.
On this issue of age, the MC is a teacher who apparently formarly worked at a laboratory of some kind, but if he's teaching then he clearly has a degree in teaching. So once again: how old is he?? Am I meant to believe he had the time for multiple degrees in wildly different subjects? Then moving in to the Principal's office, there a whole load of issues. The teacher claims it's hard for a private school to get employees, which is almost laughable to me. I have NEVER heard of a school where private schools earn less than public schools. NEVER. Unless they're literally failing financially, there is no reason they should be earning less. Then the principal's questions are extremely rudimentary, I'd have hoped we got at least a *bit* more customisation than all of 2 choices for inconsequential points. I mean, not even a "sir" option for a private school? Again, just feels very rudimentary.
However, I liked what the creator was able to do with the animations using the less-detailed models, they're very fluid. The dialogue also holds up to other games on this site, although that's not saying too much with the quality of many of them being nigh unreadable.
Ultimately it seems like a decent foundation for a game who's sights aren't particularly high, and I hope they can be reached. If more was done later on to expand I would be happy, so long as more thought was put into it and it wasn't simply a lot of words describing very little.
*DAY 4 EDIT:
Now, I'm sure you'll see in the newer comments that people are upset about some model changes, and I'd like to comment on that first. The majority of changes are incredibly minor. 90% of them are either very minor, or simply height changes. Two characters, Yui and Sadie, got complete overhauls, however they were there for essentially a minute of conversation and their models now are undoubtedly better. The only contentious change I could possibly see is for the character Georgia, who has her own scene. She is radically different to her first version. The sexual content itself plays out essentially the same, but yes I can see why there people may dislike the change. I think her also looking like Sadie with make-up doesn't help, as her appearance prior made her look distinct enough where it wasn't a problem.
Now, there are also a number of other changes between Day 3 to 4. The majority of model changes make everyone look objectively better. The lighting also appears to have improved, largely through the use of shadows that make it look more realistic. The U.I. has a greater sense of style, and feels more professional. The writing has also been improved: the grammar and syntax is better, dialogue is more natural, the humor in Day 4 in particular shows clear improvement to the original in Day 1. This all lends to the sense that RogueOne's skills are improving the longer development goes on.
One of the few negatives I'd offer is that every scene appears to be brightened. It feels like the gamma has been turned up: while the original Day 3 had a more warm color, the current version is far cooler. It's obviously personal preference, but I prefer the warmer tones, and I think it fits the game better. The biggest example of this is, oddly enough, the Georgia scene. The room's aesthetic war originally darker and warmer, which lended itself well to the environment they were in. The newer one is brighter and cooler, meaning you can see more of it despite the context of the scene warranting the opposite. The darker lighting also helped hide some of the faults in the animation, which are more obvious in the newer version (and unfortunately, the errors appear more frequent, although that may be due to angles and the aforementioned lighting). Obviously her model was changed due to her visually appearing younger (although I'd argue she had a body type similar to Piper Perri, who is 4'11" and skinny as anything while also being in her late 20s), however I feel there was probably a way to find a better middle ground, and unfortunately she looks very Sadie-esque now. The makeup is meant to make her look like she's pretending to look older, but it looks similar to the landlord/mom's makeup, so it just looks overly done but normal. The makeup DOES allow for a runny makeup look though, which is well done.
Overall, I'm improving my score from 4/5 to 5/5, as I believe the game has shown the improvements required to justify a change from 8/10 to 9/10. I will also say that the premise is relatively simple, and the score is based on how well the AVN is within that premise.