ICFs are a way of building a well insulated concrete wall out of easy to use, lego-like forms made from expanded polystyrene. Neither concrete or styrofoam are particularly green materials, but with rare exceptions all foundation technologies are pretty gross, primitive and invasive and few systems tread lightly on the landscape.
Above grade, the use of ICFs is questionable. They are serious architectural overkill- the up-front carbon load is astounding, and at the end of their life they are good for nothing but landfill. An equivalent insulating value can be achieved without such massive use of carbon and hydrocarbon intense materials.
Yet they are marketed as a green product; one brand is even called eco-blocks. Before we started measuring building materials in terms of their carbon footprint, before we worried about trucking gravel and making cement, before we measured the hydrocarbon content of our insulations, it might have been. Now a green building is one where we tread lightly, build out of recycled and recyclable materials, use as little of them as we can, and think about preconstruction, deconstruction and lifecycle.
ICFs are energy efficient for the occupant, solid and strong, and useful for foundations. However I think we are past the point where anything that saves a little money on heating is called green, the issues are bigger than that now. In such a world, polystyrene and concrete sandwiches are not green.