From an interview at Eurogamer about the novel:
Turton tried to write it when he was 21.
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It took 12 years.
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perhaps the strongest contributor to a video game feel was having a world with set rules - only, these weren't ironed out until surprisingly late in the day. It wasn't until an American publisher was interested, rules were pushed to the forefront. Call it cultural taste.
"The US edit was far more interested in the rules of the house," Turton says. "They were very specific about upfront wanting to know what these rules were. I think a lot of that is where the video game feel comes into it, by establishing the rules nice and early. In the UK edit, it felt a bit more loose around the edges, had a bit more of a dream quality to it. There were definitely rules but they weren't being explained as early.
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He would wake up each day and pick a part of the book, from his spreadsheet, he wanted to write. "If I had a day where I felt like writing a big fight scene, I'd write a big fight scene," he says. "If I wanted to write a philosophical bit, I would find a philosophical bit on my plan and write that bit.
