In the previous version, random pictures around a scene could be stitched together allowing an experience you could explore. For example, one of the original, popular photosynths allowed you to explore inside an art studio. You could look up at the ceiling, walk on various paths, move close into pictures, etc. In this new version, you're stuck on rails.

tl;dr: In this version each node has two exit points: next or previous picture. In the previous version each node had an unlimited number of exit points to other pictures.