A Microsoft operating system is working well when – and only when – it is not noticed at all. It must leave users to work without tripping over the interface or enduring a crash. It is a product that can be praised only in the absence of complaints. This is the price Microsoft pays for enjoying a natural monopoly. It is also at the heart of most of the complaints about the latest OS, Windows 8, officially released Thursday. Because it has been built to work on tablets and smartphones, it is very different from earlier versions. It must, by definition, fail at its primary duty, that of invisibility.