I would like to suggest an extra feature. Gallery-specific image sizes which can override the default image size set in settings. I frequently find this would be useful on website projects.
For example, the image size defined in Settings might be 800 x 600, but I may want to create a gallery for a different page template which uses 1000 x 800. I don't wish for my client who uses the website to have to go into Settings and change this each time, so it would be useful if you could override the default 800x600 size on a per-gallery basis, if you choose.