Everybody on Slashdot talks about how Windows 8's flaw is the Start Screen. But as someone who has used Windows 8 extensively, the fundamental problem isn't just that the start menu is now full-screen. That is just the first big jarring change you see. But fixing that alone won't solve the problem.
The real issue is that half of the OS uses the desktop UI, and the other half uses the "metro" UI. The built-in metro apps are inferior and redundant to the desktop counterparts. The metro photo viewer doesn't have as many features, you can't navigate photos in a folder. There are at least 4 wizards for adding a printer, some are metro-based and some are desktop based. System restore is another one like that, and there are lots more. There is a redundant registry area for desktop IE and the Metro IE, so some things like IE proxy settings can get out of sync between them. You can't even get to some of those settings from Metro. You can't put apps in the Startup folder.
The bottom line is that they just didn't finish the Windows 8 UI.
Look back at the Windows XP and 7 start menu. The shortcuts are usually a mess: folders with only one icon in them. Or folders with 3 icons: the app, the readme, and the uninstall. Can you remember which things are under "Accessories" versus the ones under "System Tools?" How many icons are on there that aren't apps at all? (Ex: I have a Silverlight icon - why?) The Windows 7 start menu is capped at 1/2 the screen height, wasting space and requiring scrolling. Installs typically put icons onto the desktop, the quick launch bar, and the start menu.
There are actually a lot of good improvements to Windows 8. Full-screen apps isn't a *terrible* idea necessarily. But they just haven't figured out how to offer full-screen apps with all the power of the desktop. I'm not sure anyone has figured that out yet. Time will tell.