It's not a failed experiment.
'Success' does not need to mean, "Everyone universally enjoys this XXXX".
I'm a Windows Phone user as well as a Windows 8 user. I like both of them. I like that they've combined them. It works very well for me.
The interface needs to be refined in order to appeal to more people, but that does not mean it is a failure. It just means that Windows 8 was the first iteration of something that could/should/can be very, very good.
Taking the first steps toward a goal is not failure- it's building a foundation.