Roasting fruit and vegetables tends to both intensify and mellow flavors. Obviously the texture of the grape changes - it softens. The roasting also caramelizes the sugars in the grapes and allows the grapes to take on flavors that enhance and mix so nicely with them - like the balsamic, the herbs, the pomegranate molasses. So they can taste like everything you love about a grape with new flavors added to the mix.