The overlay window looks amazing.
My only request, which has been commented on prior, is for support of Pages. In other words a parameter to say how many images per page, and then the support to scroll between pages, without the content around the tag to change.
I am now most happy.
Might is suggest a fast solution? Use this plugin: http://extensions.joomla.org/component/option,com_mtree/task,viewlink/link_id,1046/Itemid,35/
...and add tabs in your content. Within each tab, place a different gallery. Not the best solution, but could fit the bill. The pagination feature will be taken into consideration though! ;)