Kind of fun to see what Google think is cool for you.
Here's what Google said about it:
Reader Play is a new way to browse the most interesting stuff on the web, all in one place. Items are presented one at a time, and images and videos are automatically enlarged to maximize the viewing experience. You don't need to have a Google account to use Reader Play, but if you have one, your experience will be personalized. Click the "Like" button, and we'll show you other content we think you’ll enjoy. Reader Play is an experiment, and can be found in Google Labs. http://www.google.com/reader/play