Cute, funny, stylish. There are a lot of good small touches in the presentation (intentional or not, the aspect ratio feels nostalgic in how it's reminiscent of pre-widescreen video games), and the charming art is a good fit for the tone of the story. I also think the excellent prose and dialog demonstrate a strong voice. 

In terms of plot development, it's more of a mixed bag. There are interesting choices in the structure – by spending a lot of time on the main characters meeting each other but largely eluding the parts where they're actually friends, the game comes off as slightly distanced, helping it maintain the tension in the question of what the central relationship is really like. I think I like the singular science fiction element considerably less; though you get some fun parallels, it doesn't really go anywhere in the end and makes the story feel much less cohesive. There is also a sense that The Proximity Principle is about two things, whether a rules-based friendship can work and the proximity principle, which it fails to fully reconcile. Someone who only read the ending could be surprised to learn that the first theme was there at all. 

Also, this is more of a nitpick, but using 2nd person and presenting the protagonist as an audience stand-in feels weird when the sprite is visible throughout and he is ultimately kind of his own person. I wonder if giving up that angle could have made the character development stronger; in comparison, Ashley feels very nicely fleshed out with all we learn about her.

The VN is worth reading for the very good ingredients alone, even as one of those "less than the sum of its parts" cases. But in my opinion, it's not quite focused and diligently edited enough to feel like a complete success in its shortform format.