One of the coolest features of Touchwiz devices is the included theme manager. In the olden days of Android you would need to flash a custom rom after unlocking your bootloader if you wanted to use a theme. Even then most themes were Rom specific, and it could take hours to round up a theme you really liked as themes had their own threads. Eventually CyanogenMod built a theme engine directly into their Rom which gave theme developers an easy way to integrate their themes into the Rom. You could simply download from a list of themes in the Android Market and then install in the theme engine.
Samsung apparently liked this idea and decided to build the same into their Android skin. My favorite new Samsung Theme is the Android N theme. Once installed you will do a double take. Is that a Nexus 6P Im holding or is that a Galaxy S7 Edge? Everything is themed including the notification pull down, settings menu, icons, UI, dialer, contacts, calculator and more. They even included the first Android N wallpaper. To grab this theme head into the theme store and search "Android N".