Halo 4 creative director Ryan Payton has left developer 343 Industries, stating work on the game had become a "crazy endeavour".
Payton was writing the game's story and headed 343's creative team, tasked with developing the fictional Halo universe for the forthcoming sequel trilogy.
"After a few years, there came a point where I wasn't creatively excited about the project anymore," Payton told Kotaku.
"The Halo I wanted to build was fundamentally different and I don't think I had built enough credibility to see such a crazy endeavour through."
After several years at Microsoft's massive Halo studio, Payton lost interest in the project. His change in heart was partly due to seeing friend and developer Jake Kazdal working on indie RTS Skulls of the Shogun.
"I never thought I'd get to a point where I was so drained," said Payton, who was at one point diagnosed with severe depression. "That was when I knew I had to do something else."
"I think time is the most valuable thing we have and I've decided that I'm not going to waste one more day working on something that doesn't speak to my values," he said.
Payton already has two new titles in the works at his own start-up studio Camouflaj, and big ambitions for the future.
"Some people say I'm crazy, but I want to make a game that one billion people play at once, and it's something that hits them harder than a great book or film," Payton concluded.