If powerful tagging of images is the most important feature/requirement of your gallery, then this tutorial demonstrates a performant way to achieve it in MODX CMS.
My latest assignment was a MODX site featuring a thumbnail gallery. With the specific requirements of the project, the first snippet that came to mind was the venerable all-in-one toolbox called getResources and the sister-snippet getPage. Here's a tutorial on the installation and usage.
Really simple slideshow management in MODX CMS.
A quick MODX CMS tip: how to make the Gallery snippet accept (and render) the &outputSeparator property.