I have used Windows 8, and I don't like it one bit. It just seems poorly designed, apart from anything else. the new Start Screen and the Desktop are now practically two completely seperate operating systems - one that's based on WinRT and runs Windows Store Applications (or programs, a term I much prefer), and one that runs native programs. The former is basically a poor copy of Apple, and the latter is good ol' windows 7 but with a worse visual design and no start menu.
The gestures in the Start Screen work just find, and I can see how they make total sense on a touch screen device - but the thing is, the bast majority of computer hardware is (and for the forseeable future shall remain) resolutely not-touchscreen-based, and using these gestures with your mouse just feels weird and unintuitive. One of my customers the other day summed it up perfectly when I explained you needed to click and drag from the top of the screen down to the bottom to close a program: "Why can't I just click the red X?" ... "because there isn't one." ... "Oh."
Back to poor design, the two parts of Windows 8 don't seem to mesh together particularly well. Take, for example, the PC Settings in the Start Menu and the Control Panel in the desktop. They're both there, and the both work fine. The former has FAR fewer options than the latter, and can only be used to control the Windows Store programs (install/uninstall etc). The latter is still as powerful as always, but because of the lack of a start menu cannot be found on the desktop unless you make a shortcut there: unless you Search for it in the Start Screen, you wouldn't even know its there. This is the only place you can manage desktop programs. This does not seem to me like intuitive design.
The whole Windows Store locked down thing annoys me, I don't like anyone telling me what I can or cannot do or install on/with my computer. It's just wrong. If they want people to develop programs for their ugly, poorly designed new interface, they need to make people want to do so, not put barriers in their way. Also, I admit I've not researched it, but how on earth do you test your Metro programs during development if you cannot install them without Microsoft's prior approval?
Because of my job as a salesman at an electrical retailer, I had to do Microsoft's official retail certification program, teching me all the new selling points and how to use it etc. I found it EXTREMELY amusing how the official answer to the question "Won't the new Start Screen get in the way of the programs I usually use?" is "With one click, the familiar desktop is there for when you need to be more productive." They just admitted themselves that the new interface is counter-productive.
Finally, the changes which have happened are just a taste of what it likely to come if they decide this was a success - Windows 9 will probably relegate the Desktop to a "legacy" feature you have to pay extra to buy (like how you now need to pay extra to get Windows Media Centre in order to play DVDs!) so that the majority of people will be forced to use their new interface and buy their programs through the Windows Store.
Not to mention that Windows 8 requires that the BIOS on new computers support something called Secure Boot, which is designed to physically prevent the user from installing a different operation system if they so choose. Admittedly, the current Windows 8 hardware requirement spec requires that it be possible to disable this feature, and Microsoft states it's designed as a security feature to stop Viruses infecting the boot path. Fair enough. But Windows RT tablets are required to make it impossible to disable the feature. Now, that is inexcusable, and clearly shows where Microsoft wants to take this.
There is a lot more I could go into, but that ought to be enough fuel for the fire.