With SplashCase for Mac you can create custom slideshows fairly easily. While not the most advanced slideshow app out there, it is a good choice for amateur photographers, as it has an easy-to-use interface and nice functionality. Be ready to invest in the paid version of the app, though.
SplashCase for Mac installs as a free trial version with a nasty limitation: a large, conspicuous watermark across your slideshow. Therefore, to use this app properly you have to upgrade to the paid license. Clicking on the "Create Slideshow Settings" button will launch the app's setup wizard that will walk you through the process of creating your own slideshow settings, allowing you to choose the size of the image, background, and number of images per screen, among many other options. This preset settings option is automatically saved, and you can use it later with other slideshows. Creating a slideshow is easy; all you have to do is import the folder containing images into the app; but before you do, the app will let you set the size and compression of your slideshow thumbnails using two sliders. You also need to select one of the preset settings options you've created, and you're ready to go. To test the slideshow feature we used a folder of vacation photos (1GB in total), and the app took about two minutes to load them and create thumbnail images. Once they were loaded, the images displayed as a slideshow in the app's preview window.
Whether you're a photographer, graphic designer, or researcher, SplashCase for Mac has some nice features for you. To enjoy this app, though, you will have to buy the paid version; the annoying watermark makes the trial version good only for testing the app's features.