This isn't an operating system, but I've been playing with Flex Launcher recently and it's been working really well for my needs. From their Github page:
Flex Launcher is a customizable application launcher and front end designed with a TV-friendly 10 foot user interface, intending to mimic the look and feel of a streaming box or game console. Flex Launcher allows you to launch applications on your HTPC or couch gaming PC entirely by use of a TV remote or a gamepad. No keyboard or mouse required!
i use it as a lightweight launcher for my gaming PC as well as my HTPC. It does include gamepad support (needs to be enabled in the config file) and works really well with a USB remote.
You can customize the look quite a bit. You can use whatever images/icons you like. For example I've just been using boxart for games. You can also define submenus kind of like folders. The configuration is manually editing a file so you won't be able to use a GUI. It's not too dificult to modify though.
https://github.com/complexlogic/flex-launcher/blob/master/docs/configuration.md#configuring-flex-launcher