I've been testing Windows 8 RTM on a tablet, and it's clear that as a tablet operating system, Windows 8 is a winner. Here's three reasons why it may be better than the iPad and Android tablets.
Quick information at a glance
Windows 8 draws its design inspiration from Windows Phone, and sports big "live" tiles that display constantly changing information. Social media updates, news, email, calendar events, and more are delivered straight to those tiles. At a glance, you see all of your important information, and get more details by tapping a tile. iOS and Android are app-centric rather than information-centric, and have nothing like this.
You can get real work done
Add a bluetooth keyboard, a wireless mouse, and a stand, and a Windows 8 tablet becomes essentially a traditional PC. Sure, you can do the same thing with an iPad or Android device, but why bother? Windows 8 runs productivity applications, notably Microsoft Office. iPad and Android don't.
You can use your favorite applications
iOS and Android tablets run apps rather full-blown applications. On Windows 8 -- the full Windows 8, not Windows 8 RTM -- you run true applications, not stripped-down apps. Whether it's Office, Photoshop, or any other application, you can run it via the Desktop. Windows 8 also has its own native apps, and you can run those as well. But it's the only tablet operating system that lets you run both big applications and smaller apps.
As for Windows 8 as an operating system for traditional computers, it's not a winner, because its designed more for tablets than traditional computers. For more details, see my review, Windows 8: Still a two-headed beast.