We love OS X and Yosemite has some great new features, but a way to quickly view a Folder of images is not one of them. Slides is designed to do just that. Finder takes 9 mouse/keys actions, Slides only 1, and it has preferences.
Drag and drop the Folder onto the dock icon and you are watching the show.
This App is not designed to generate fancy slideshows like iPhoto, Keynote or iMovie. It just shows the images one after the other.