Actually his explanation is quite a simple one. Valve "stopped making epic, triple-As," and turned to episodes. That just wasn't enough to satisfy Antonov, who has worked at Arkane on Dishonored.
Valve grew to such a size that it lost that "small, core team" feel which Arkane provided the Half-Life 2 art wizard, as he worked on The Crossing and Dishonored.
"I left precisely when they stopped making epic, triple-As, which was Half-Life 2," Viktor Antonov told Eurogamer in an interview. "Since then, they were episodes." Two episodes released for Half-Life 2 with a third left seemingly in limbo. Valve lost a certain energy when it continued to grow, he says, so it was time to move on.
"Valve is a great place, but I'm interested in projects, not in companies. I went to Valve specifically for Half-Life 2. I went and I collaborated with Arkane to do The Crossing and Dishonored. I put the project above everything else."
"Valve has grown into a much bigger company," he continued, "and what I really enjoy about the philosophy of Arkane is that it's a small, core team that does risky creative projects. And when I went to Valve, they were a small company. They've grown now, they're much bigger, and I'm interested in a certain level of creative risk taking and a certain energy that can be compared to jazz, jamming or rock n' roll, where it's small, it's intense and it's about making revolutions in the media."
As of now Antonov works as a visual design director for Zenimax, which is a considerably bigger role than his time spent on Arkane's Dishonored. Antonov now oversees the visual design of all projects that fall under the ZeniMax roof, which include Bethesda, id Software and Arkane.
"It causes a lot of surprise that anyone would leave Valve. I left Valve, and all my good friends from there, for the specific reason that I had spent six years of my life on one single project, and that's a lot," Antonov explained. "And, as an artist, I wanted to express myself in a whole variety of ways. So, since then, I have done two feature films, TV series, I've designed a third feature film, I have done three separate games and an illustrated novel, as an independent author."
It seems he doesn't entertain the thought of one day returning to Valve. "No, no," he said. For those with a love for concept art you can check out his works on his website, which includes Half-Life 2 and Dishonored.
Dishonored releases on Xbox 360, PS3 and PC October 9th in the US, 12th in EU.