All of what kk said plus: 1. Real Booleans. Then we can actually see what we're modelling. 2. Collision detection. Those bounding boxes have got to be useful for something. 3. Faster render engine. Yeah, I know kk already said it but it's important. 4. Everyone loves the interface; it's a stroke of genius. Over the last five years, I've convinced at least a dozen people to buy Bryce on the interface alone. Engineers want four-pane orthogonals: artists want Bryce.