1) With some template modifications you can add the ability for registered users to comment on your photos. Ratings could be built as an option, but does not exist that I know of.
2) There is already in the forums a template modification that will allow you to open a photo large size in a new window
3) I believe that you can adjust image conversion settings in ImageMagick to add a watermark to the images
4) Uploading is included, to upload 1 image at a time. Also available is a WebDav module that allows you to a desktop application to load images directly. This would be the best bet for large amounts of images. 5) You can allow registered users to create their own images with a few simple changes to the roles and policies.
All that being said, if you are truly just in need of a gallery, and not any of the more powerful content management functions for other types of content, you should consider Gallery 2 (http://gallery.menalto.com/) as it is a simpler solution to present just a gallery, and includes all of the features you mention.
