Nielsen tested Windows 8 by having 12 experienced users try the new operating system 8 on both PCs and the Surface RT tablet.

Concluding the OS to be “weak" on tablets and "terrible" on PCs, Nielsen was particular unimpressed by the different interfaces for tablet and desktop, the "low information density" on tablets (essentially very little information on the screen), and the flat Windows app icons.

He also experienced problems with gesture control, Live Tiles and "generic" Charms.

Power users of Windows 8 will also be dissatisfied, according to Nielsen's report, which stated that Windows 8 doesn't support multiple windows on the screen at the same time, a problem which is apparently more frustrating on Windows 8 PCs.

However, the user interface guru did conclude that things are at least likely to get better on future Windows tablets.

“Although Win8 has usability issues on tablets, there's nothing that a modest redesign can't fix.

“In fact, usability could be substantially improved by revising the application guidelines to emphasize restrained use of active tiles, higher information density, better visibility of key features, and many other usability guidelines we've already discovered in testing other tablets.

“I have great hopes for Windows 9 on mobile and tablets. Just as Windows 7 was "Vista Done Right," it's quite likely that the touchscreen version of Windows 9 will be "Metro Done Right."