Here's what's new, as well as what's changed or been removed in this latest release:
- Simple Image Gallery (free) is now PHP 7 compatible (sorry for the wait).
- fancyBox has been upgraded to the latest and greatest release (v3). This new release has a better modal/lightbox preview (which also includes a navigation grid for faster browsing) and it's also mobile friendly.
- Every external dependency (including jQuery in Joomla 1.5) is now loaded over cdnjs.com, an HTTP/2 CDN provided by CloudFlare for such projects.
- Plugin parameters have been refined: there is no jQuery selection for Joomla 3.x (as the one included by Joomla itself is what's used by fancyBox) but only for Joomla 1.5 & the "advanced" parameters have been merged with the main (basic) parameters in a single tab (in Joomla 3.x) or slide (in Joomla 1.5).
- Other minor bug fixes (PHP warnings/notices) and code improvements.
Please keep in mind that Simple Image Gallery (free) v3.5.0 is the last release to support Joomla 1.5.
If you are on Joomla 1.5 it's also important that you enable the "Mootools Upgrade" system plugin, otherwise both fancyBox and any chosen jQuery library (1.8+) will conflict with the older (stock) Mootools included in Joomla 1.5.
Starting with the next update (v4), Simple Image Gallery (free) will be strictly compatible with the latest release of Joomla at the time.