Okami in its beta version was much different from the final one. The game was originally planned to be rendered in a more photorealistic 3D style. However, Clover Studios determined that the more colorful sumi-e style allowed them to better convey Amaterasu’s association with nature and the task of restoring it. This change did not increase the game’s performance. You can play a video clip of Amaterasu in her original realistic style after beating the game. – [info from Wikipedia]
Also, on 1UP we can read an interview with Kamiya that talks about the early prototype of Okami:
“When I first started talking about it with [producer Atsushi] Inaba, the only starting point we had for Okami was a game that depicted a lot of nature,” he said. “I couldn’t say ‘I don’t know if this’ll be fun or not’ because than nobody on the dev team would be enthusiastic about it, so instead I was like ‘This is gonna be great! I know it will!’ So eventually the discussion shifted to a wolf running around, and we made this minute-long video depicting a wolf running through a field and trees sprouting up behind him and I told the team ‘See, isn’t that neat?'”
Eventually Okami made it to the prototyping stage, but Kamiya’s problems didn’t end there. “Our first test run was incredibly boring to play,” he recalled. “I was grinding my teeth at night, I was so worried. At one point, we were so far off-track that it had turned into a simulation game — you had hexes and trees sprouted on them. It was total garbage. A couple of devs said to me afterwards ‘Something was definitely wrong with you around that time, Kamiya!'”
Thanks to Robert Seddon for the contribution!