In comparison to other galleries Phocagallery has the advantage of being 1.5 native, not a bridge and capable. The code is solid, it's simple to use and install and has good features. I expect it to continue to mature and become THE gallery for Joomla 1.5. I used RSGallery2 for a short time and have been using the Gallery2 bridge for years. Phoca doesn't do everything the others do yet but the code is cleaner and new development is happening much faster. I think Phocagallery is the future.
With Phocagallery 1.8.6 you can now rotate images and recreate thumbnails. In addition to the already present features of having as many categories as you want (and nested too) with the ability to have a theme you have a good base to create nice galleries. In the future I'd like to see more powerful theming, and some new modules..