It's still full-screen and lacks any of the visual context of the desktop. Something like GNOME3's fullscreen Activities screen is better; when you open it up, it has little mini-screenshots of all your open windows, and you're not losing things like the taskbar (because it doesn't have one). You still have the top bar, which ties it into the system.

Opening the Windows 8 Start screen loses all the visual context - your taskbar disappears, your windows disappear, there's nothing to tie it into the desktop, it feels like an entirely different system from the one you were using a second ago. And that's before the fact that how you interact with it is entirely different from how you interact with a desktop app, which is the final wedge.

But that's a failure of the split-experience, not metro itself.

Sure, but they can't drop support for everything built over the past couple of decades just to have a new interface, so it is the fault of introducing Metro into Windows 8. To get around the problem, they could've had plenty of integration from the start - having the taskbar throughout Metro would be a brilliant start, and something familiar.

Luckily, they're integrating Metro into the desktop properly now, so the entire system will be usable.

Tiles can be resized to be small, medium, large, and x-large sizes.