I mean, the backgrounds are photos, the girls are basically all the same with different hair, the pictures are low-res and the style is not consistent.... but the fact that there are so many girls and they all get plenty of solo time instead of throwing them all into an orgy, the soft pastel-like colours and the amazing job the artist did with posing and with giving the girls sexy and realistic bodies just makes this feel so real.
It's one of those old dating sims where it just felt like a real romance. Nothing I see nowadays is anything like this. Even in romance-heavy games the characters and scenes feel artificial. I don't know, maybe it's just nostalgia because they're high-schoolers and I played this back in high-school so it takes me back to young love times.