Each character in the game took about a month and a half to design, with a few exceptions. Poseidon was a big challenge -- making a character out of water took a lot of iterations between the art team and the technical guys. The Titans in the game, however, were a real challenge: Izzy talked about designing even Kronos' skin pores, since they were basically big enough for Kratos to crawl through ("Actually, that's pretty gross if you think about it," he laughed).
The team also talked about how their designs sometimes influenced gameplay. Izzy was given the task of coming up with designs for what became the Nemean Cestus weapon in the game, and the original idea called for two hammer, boxing glove, or brass knuckle-style objects to be used on Kratos' hands. After a little research, he found this weapon called a cestus, and then gave it a Nemean lion design, and he believes that look influenced a lot of the grabbing gameplay now found in the finished game.
Finally, they spoke about how hard it was for the art team to stick to the Greek style -- the developers were very concerned all throughout the process that the game never fell into the fantasy realm, and never strayed away from the starker Greek style of clothing, weapons, and architecture. While some of the artists were God of War veterans, many of them hadn't worked on the series before, and often, they would make a concept only to have it rejected for being too flashy, too fantasy, or even too Roman rather than being specifically Greek. The challenge there, they said, was to stick with the Greek myths, but give them a unique spin. The Satyrs specifically were mentioned as an example of a character that has a long mythology, but that the art team tried to put their own unique touch on.
It was an interesting talk. The art team isn't directly involved in the product we see in our PS3s -- they joked that they get to crunch at the beginning of production, so that by the time the coders are working hard, they get to go home early, because everything's already designed and done -- but they do have a lot of early influence on the look and feel of the final game. Check out the gallery above to see how they tweaked and designed some of God of War III's characters and set pieces.