The trick is to make the contrast on the metallic surface flat and subtle, while lights are used to create interest. But 343 tends to make them shiny and overpopulated with lights and textures to make them seem "alive". However, it ultimately ends up cluttered, noisy and distracting. It's especially problematic in gameplay because we interpret it as a multi-angled surface, which makes it difficult to predict how a grenade might bounce.
Compared to Halo 3's Guardian, where everything looks flat despite having a fair amount of details.