I'm not really in to these Windows 8 discussions, basically because I'm not using Windows myself, but the main argument against Windows 8 that I have come across so far was that there are two different interfaces.
As I understand this new interface is called the Metro interface, which (without having it used) looks promising, bu t is totally different than the old Windows interface (which I have used).
It seems to me as if Microsoft couldn't finish the Metro interface so it was a good replacement for the old interface, so they just kept the old interface as a backup.
But then again, this is coming from someone who hasn't used Windows 8 in any way.
In the new Metro UI you cannot run traditional desktop apps - these that use Windows API - and there are loads of them around already. So keeping the old UI system in parallel is the only viable option to get Metro slowly adapted.
As I understand this new interface is called the Metro interface, which (without having it used) looks promising, bu t is totally different than the old Windows interface (which I have used).
It seems to me as if Microsoft couldn't finish the Metro interface so it was a good replacement for the old interface, so they just kept the old interface as a backup.
But then again, this is coming from someone who hasn't used Windows 8 in any way.