Apart from Europe, the number large, powerful non-signatory countries is pretty significant: US, China, India, Russia, Iran, Saudi, Egypt, Turkey, Indonesia, and more.
I've always thought it is interesting that the concept of international law is by definition in conflict with the de facto anarchy of international relations. I've always had mixed opinions on the topic, simply because you can look at an institution like the UN, and see that it functions much more successfully as a simple forum than a deliberative body. The idea that somehow we are going to implement something as difficult as a criminal court on an international basis seems... very idealistic. A court like this always seems sensible at first glance, but I'm not sure it can really exist effectively at all over any serious time horizon.