I can't give a full answer to what he means by creative suffering of God just yet, since that will be unveiled through the entire book. The impression so far is that he critically uses process philosophy, being skeptical of some of its core doctrines. He embraces a form of kenotic creation, namely that God willingly limits himself when creating to offer real freedom. So unlike in process theology, this freedom and the suffering that results from it, is not a metaphysical necessity but rather God's creative act. He then wants to place God at the center of this evolving community of organisms (rather than above it as in the hierarchical reality in medieval philosophy). God participates in sympathy with his creation.
It will be interesting to see how he will present the eschatological victory over suffering. The problem coulb be that if there is no good eschatology is that it can devolve into a sentimental and rather tragic view of reality.