Showcase thousands of photos with simple transition effects, using Simply Slideshow
Simply Slideshow is a free program that will let you play thousands of photos without unnecessary transition effects and with high performance.
The program features minimal options, such as full screen or not, some simple transition effects, duration of each photo, etc.
I personally miss an option to fit large photos to the screen, but not enlarge small photos.
Simply Slideshow is very easy to use and will do just that, it will let you prepare and enjoy as fast as possible a slideshow of your photos.