The entire rendering engine is brand new for Xbox 360 with high dynamic range lighting, light scattering and dynamic self-shadowing.
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We have a dedicated grass shader that draws blades and scatters them across grassy areas so now our fields and verges have more volume and the straight-line edges are much more blurred. Every material in the game is faithfully represented - rubber absorbs light but has a slight sheen, brushed aluminum even has the brush marks on it and carbon fibre weave reflects light differently depending on how you're looking at it. We should hit 60 fps still with 20 bikes on the grid.
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We have a light scattering algorithm that models the way light bounces off of particles in the atmosphere. Effectively, it's really clever fog but what it does is make stuff in the distance get lighter just like it does in real life. This massively improves your perception of depth in the game. It also makes things look a lot more realistic. Everything can shadow everything else in the game. So now, the rider casts a shadow on himself and the bike for example.
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The bikes and riders together are in excess of 40,000 polygons now. That's five or six times what they were in GP3 and then there are normal maps and up to 6 layers of shader on every material. We don't talk about textures and models any more, we now describe materials using shaders so every surface on the bike can look and shine differently.