My 2 cents worth (talking from a desktop perspective, not tablet):
Windows 8.1 is a good OS. It is stable, integrates well in active directory, runs just about any programs that was running on Vista and 7. The biggest issue by far is the modern UI. It does not make sense when the OS is used on a desktop or laptop for that matter.
If MS decided to listen to the customers and managed to detect the hardware platform and docking status to present either the classic desktop with a real start menu if no touch screen is available, if it is a desktop chassis, if it is docked or the modern UI if it is tablet chassis and it is not docked, the OS would be much more accepted.
We are about to roll-out windows 8.1 in the corporate environment. Classic Shell is our savior. From a user perspective, with classic shell loaded, it is like using XP or 7 (close enough), no re-training needed.
As a tablet, I am not a fan. Android and IOS are far friendlier to use, but they don't run our corporate apps...
Maybe Windows 9???