Here is a cute idea for a slide: negative lettering space. has a full tutorial how to create this effect here. It is easy to copy in PowerPoint: start with a word in a huge font on a page, set the font color light grey (or another color with a light contrast to your background), fill the page with the images you want, and as a final step delete the text or color it the same as your slide background.

Here is a search for earlier posts with a "can't see the forest through the tress" type of concept.