Two interfaces, a lack of multiple windows and a flat visual style that hinders "discoverability" have been singled out as Windows 8's more significant issues by Jakob Nielsen, a usability consultant and former engineer for Sun Microsystems. Nielsen goes so far as to say that trying to combine a tablet and PC interface into a single operating system was a "strategic mistake" on Microsoft's part.
Nielsen goes into more detail on Windows 8's deficiencies both in an interview with Computerworld and a blog post on Use It. Speaking to Computerworld, Nielsen states that Microsoft's vision of a tablet/desktop OS hasn't worked out:
"That was the true strategic mistake, that they could do 'one Windows' on both tablets and PCs ... Windows 8 has low usability, amazingly low usability."
Nielsen goes on to say that Windows 8 takes control away from users, something they've grown accustomed to with previous iterations of the operating system. He's also not a fan of the low information density that Metro apps seem to have adopted, comparing apps for Bing Finance and the LA Times with their website counterparts:
Despite running on a huge 10.6-inch tablet, Bing Finance shows only a single story (plus 3 stock market quotes) on the initial screen. The Los Angeles Times is not much better: this newspaper app's initial screen is limited to 3 headlines and an advertisement. In fact, they don't even show the lead story's full headline and the summary has room for only 7 words.
It's still early days for Windows 8, but it's hard to see Nielsen's concerns being addressed with a service pack or platform update. As for the apps themselves, there's still plenty of time for tweaks, improvements and innovation from third-party developers.