Subfolders are done using the new PFS system
which supports unlimited subfolders. You will need this in order to be able to use subfolders in the gallery.
Prev/next buttons are included with the lightbox script which you have to install manually (download here
Oh and I forgot to say it users Smart Image Resizer
for generating thumbnails. You will need to put the image.php inside /datas and rename it to thumb.php.
Basically, this plugin isn't for everyone just yet. It requires some know-how to get it all working. In the end it will be compatible with Cotonti 1.0.0 Renaissance (which will include the new PFS and dynamic thumbnail feature).