Well-known interface guru Jakob Nielsen has put Windows 8 through user testing on PCs and tablets, and his conclusion is a stark one: Windows 8 is bad on tablets, and even worse on PCs. He blames dueling interfaces, reduced "discoverability," "low information density," and more.
Neilsen tested Windows 8 by having 12 experienced users try Windows 8 on both PCs and Surface RT tablets. His conclusion is that Windows 8 is "weak on tablets, terrible for PCs." (You can read his report here.) His high-level summary is this:
"Hidden features, reduced discoverability, cognitive overhead from dual environments, and reduced power from a single-window UI and low information density. Too bad."
His first findings have to do with the dual nature of the Windows 8 Start screen and Windows 8 native apps versus the Desktop, what he rightly calls "a tablet-oriented Start screen and a PC-oriented desktop screen." He says:
"Unfortunately, having two environments on a single device is a prescription for usability problems for several reasons:
* Users have to learn and remember where to go for which features.
* When running web browsers in both device areas, users will only see (and be reminded of) a subset of their open web pages at any given time.
* Switching between environments increases the interaction cost of using multiple features.
* The two environments work differently, making for an inconsistent user experience."
Nielsen notes that on the Windows 8 Start screen interface, you can't easily have multiple windows open simultaneously, which presents a serious problem:
"One of the worst aspects of Windows 8 for power users is that the product's very name has become a misnomer. "Windows" no longer supports multiple windows on the screen. Win8 does have an option to temporarily show a second area in a small part of the screen, but none of our test users were able to make this work. Also, the main UI restricts users to a single window, so the product ought to be renamed 'Microsoft Window.'"
Nielsen also warns that because the Windows 8 design is now "flat," users get confused about what can be clicked on and what can't. Icons, he says, "are flat, monochromatic, and coarsely simplified." He concludes:
"Icons are supposed to (a) help users interpret the system, and (b) attract clicks. Not the Win8 icons."
Nielsen points out that Windows 8 native apps feature very low information density, meaning that there is very little information available at any time on the screen, a particular problem on tablets, whose users will probably turn to Windows 8 native apps more frequently than do users of traditional PCs. He concludes:
"As a result of the Surface's incredibly low information density, users are relegated to incessant scrolling to get even a modest overview of the available information."
He has a lot more to say as well, essentially all of it bad. He criticizes "error-prone gestures," problems with Live Tiles, and Charms as being too "generic."
I think many of his criticims are on target, although I don't agree that Windows 8 is "weak on tablets." In fact, I think Windows 8 on tablets is better in some ways than the iPad and Android tablet interfaces, because Windows 8 is more information-centric than they are.
As for Windows 8 on PCs, I think he's right. I've said from the first time I looked at the earliest versions of Windows 8 in the development process that it was a mistake to have a single operating system for both tablets and PCs. Nielsen concurs, saying:
"The underlying problem is the idea of recycling a single software UI for two very different classes of hardware devices. It would have been much better to have two different designs: one for mobile and tablets, and one for the PC."
One thing he didn't focus on is the poor quality of the Windows 8 native apps, apart from their low information density. The Mail app is far less useful than Outlook, or the Web-based mail services Gmail or Outlook.com, for example.
This isn't the first time Nielsen has criticized Windows 8. Previously, he said that with the new interface, users of traditional PCs are ""essentially being thrown under the bus." He reiterates that exact criticism here, and I think he's right. If you're interested at all in interface design and Windows 8, I strongly suggest reading his report.