I don't know about you but I like a visual surprise to great me on my desktop everyday. Chrome OS does have a "surprise me" feature built in but it cycles through all the wallpapers that Google installs + any you have added. I have a folder of over 3000 wallpapers that I like to scroll through so I wanted a solution that would let me pick that folder and only see my wallpapers. A quick Google search later and I found "Wallpaper Rotator for ChromeOS". This great little chrome addon will allow you to choose any folder and set how often you would like the wallpaper to change. Works great for me!
Hope you enjoy!