Amazing! I find it extremely fascinating that somebody is able to create entire operating system. Not a easy task!
It’s not easy, but it’s more approachable than many realize. Much of modern operating systems are the hordes and hordes of drivers; the fundamentals aren’t terribly complicated; just lots of detail.
Then there is the question of what one means by an operating system. While I'm sure that most people would agree that much of the software shipped with Windows, Mac OS, or the typical Linux distribution isn't part of an operating system proper, few would agree upon where the boundary lies.