3
I know this isn't what you were asking for...
I use
XoopsGallery (version 1 series) myself. My only beefs with it are the less than glamorous templates (which I could make better if I'd get off my lazy butt and do it) and the flat structure for category storage. No matter how many categories/sub-categories you define, they all end up as folders in a single directory on disk. This isn't a big deal for any gallery that I've seen people use. My gallery, however, has tens of thousands of pictures across hundreds (probably thousands) of categories. Needless-to-say, parsing all of these takes time.
...just my 2 cents.