Uncharted was originally intended to be a fantasy game with elements from Lord of the Rings world, but Sony changed that after witnessing the success of gritty shooters on Xbox 360.
The info was revealed by former Naughty Dog environment modeler Don Poole, who said that they "were talking about a more 'realistic' game in terms of how it was modeled and rendered but the concepts were much more far out. One was a forest world where the antagonists lived underground."
Before Uncharted, Naughty Dog was famous for Jak and Daxter and Crash Bandicoot, both of which are known for their cartoonish style.
"It had elements of [Lord of the Rings author] Tolkien in for sure," Poole continued. "Sony kept pushing for a more realistic game in all respects. The market had changed a lot by then. The demographic was older and gritty shooters were really dominating. Sony wanted very much to get into that market share; it pushed all of its developers in this direction."
"So the big push from Sony, not just at Naughty Dog but at all of Sony's development companies at the time, was to craft games for PlayStation 3 that were much more realistic. The pressure from Xbox's success with gritty shooters was a very real force on our direction at that time."
Of course Sony's orders didn't sit well with all of the design and development teams, but in the end they all had to yield.
"We had a lot of internal grumbling about the realist bent. More of the old dogs were from the Crash and Jak era and preferred that more whimsical style. But alas, that was a losing battle," Don Poole reminisced.
We have no way of telling how Uncharted would have been like without Sony's intervention, but the success of Uncharted series is proof enough that - for once - Sony's decision was the right one to make.