Include the ability to add nested folders into a slideshow so that the contents of each folder is shown.

The "Add All" button at the right of the File List has a menu where you can select the "Add all including subfolders" item. This allows you to add the pictures of the selected folders and its nested folders to the slide show project.

Use the Tools | Folder Player menu if you want to play a slide show from pictures of the selected folder (including the subfolders if it’s necessary) without creating a project.