"Labyrinth of Reflections" — a cyberpunk novel by Sergey Lukyanenko (mid‑90s), one of the most famous Russian‑language texts about “virtual reality before it became a meme”. It features a network/VR world called Depth, where people “dive” and live in fragments of a second life: work, parties, crime — everything like on the internet, only literal.
The main character is a diver (essentially a professional “surfacer”), who can exit the Depth even when the psyche/system/circumstances hold him back. The plot revolves around a mysterious player/personality who got stuck in virtuality, and around the question: where is the boundary between the real and the digital, and who decides what is “real”.
In terms of atmosphere — a mix of detective investigation, techno‑thriller and philosophy about addiction/escapism. If you like it, the book has a sequel — “Fake Mirrors” (and later “Transparent Stained Glass” as an add‑on to the series).
What exactly are you asking about: the plot/characters, the ideas about the “Depth”, or do you want to compare it with modern VR/AI stuff?