The OP has already stated his view, but just to clarify for anyone else who's yet to try Windows 8 - if at worst you don't like the new start menu ("screen"), then it takes 5 minutes to install a free utility to put the old start menu back. And if you don't like the full screen "Windows 8 apps", you can just ignore them, and you've got something that works just like Windows 7 (along with benefits such as faster boot times, improved task manager, better/simpler backup, lots of things built in as standard from anti-virus to mounting ISOs). Even if one thinks there's no advantage, I don't see it can be worse.
It also seems hyperbole to claim it's unusable - I didn't like the start menu introduced with Windows XP, but I didn't say it was unusable, I simply switched it to be like the Windows 2000. I sometimes wonder if some people accidentally got a completely different version to me...
You should not assume too much. My point is not about liking or not liking one or the other. It's not about not being able to use a tile interface instead of a start menu.
It's about a system that has two different user interfaces and none of them is fully functional or works well, or interacts with the other in a seamless manner. The desktop interface has been deliberately "broken" (presumably to convince people to use the tile interface) and the tile interface is neither fully functional, nor ergonomic. Heck, it doesn't even let you place tiles where you want them, even for that Windows must be smarter than you are.
You want to use the tablet-optimized interface Metro because you have a tablet? Sure. Except a good number of "standard programs", say, for example the calculator simply don't run under Metro. You have them listed as "app", certainly, but they launch on the desktop. Switching to desktop always takes noticeable time, too. Not like it's several seconds, but it's just noticeable enough to be disturbing. What a crap.
Live tiles and notifications when the screen is locked. Awesome, except it's total shit. I tried this with "Mail", sent a test mail to myself from the desktop, and guess what, nothing happens. No notification until you log in again. But hey, at least all the Facebook/Twitter crap is built in, and sure enough the stuff you need the least in your life works, too.
Eventually you discover the "We sign you into Messenger automatically whenever you turn on your tablet" when you hover over the chat app. Wait, what? Fuck, that is not what I want. Of course you cannot uninstall the messenger applet without also uninstalling mail and calendar. And you cannot uninstall the Microsoft Store either, or prevent it from running in the background, even if you never intend to buy anything from it. The Kindle app permanently runs in the background, too. I don't intend to ever use Kindle, if I wanted Kindle, I'd have bought the $69 tablet from Amazon, what the hell?
You can add another user, but you cannot manage users, except if you launch the control panel on the desktop. Shame that the desktop controls are so small you need to do everything 5 times when using "touch". Similar is true for 2 dozen other system settings. No problem setting up the dumbified express stuff, but woe if you need to change something later. This means using the desktop and touch-navigating a UI that will do anything, except what you intended. Maybe it works if you have fingers like a girl, I wouldn't know.
The desktop is simply not designed for "touch", and even less so on a high-res tablet. If at least they'd be smart enough to launch desktop mode in high-resolution profile (which has been supported since Windows XP!). But of course that's deliberate, to discourage people from using the desktop. Right-click when you don't have your pen ready? That's a patience game. Of course you don't need to right-click, do you. Except all the time in a web browser, or whenever you want to do something in the tile interface that is not "launch".
You find another parade example of how mishappen Windows 8 is in its backup functionality. Of course everybody uses Skydrive anyway, right? But what if you don't want that, or if you want a real backup, including system restore and such?
There are two different systems active under Windows 8, one is "file versions" and the other is the same as you had under Windows 7. Microsoft did not even bother to change the window name, it still shows "Windows 7" in its window title. However, they did bother to botch with it. Other than under Windows 7, you cannot create a system restore disk on your SD card or on your USB stick, because Windows 8 will complain that it needs a DVD writer for that (Win 7 works just fine with a plain normal USB stick). Plus, once you have used Win 7 recovery, you cannot use file versions any more, because it will tell you that you can only use this if the other is disabled (but it gives you no option to do that!).
All in all, Windows 8 is simply not finished and not polished. It is Windows 7 with a half-finished touch interface added, and some Facebook/Skype stuff slammed on top.
The only reason why one would use it (and the reason why I bougth it) is that Android is even worse. Android is a Java toy with a Google browser.
Windows 8, on the other hand, is at least "Windows", so your programs will run (as bad as they'll run, but at least they do run), and you can program it without being forced to use Java and learn a completely new API. Of course that's only true if you never plan to use the Metro interface...
Login gestures, what a great idea. Except it takes me 3-4 attempts every single time. How complicated can it be to draw 2 lines and a circle? You wouldn't think there's a lot one can do wrong.
And of course Windows 8 boots lightning fast. Or so the propaganda says. My Win 7 desktop is up in 9 seconds whereas my Win8 tablet takes close to 1 minute. One is admittedly a muscle-desktop and the other is a puny Atom tablet, but still. Close to 1 minute for doing nothing but initializing a few drivers and swapping in a kernel image is not what I'd call "fast".