I think there's just little details that make Cycles4D node systems really great. Like for example, color coding (for both, nodes and their inputs), intuitive grouping, auto-snapping of connections, ability to preview individual node output, etc.
Again, little things. But they really add up.
Plus it's just a really feature-rich node system. I feel like there's a node for almost anything I can think of needing. I've created a number of materials with Cycles4D that i haven't been able to build with any other renderer. And that's a powerful thing.