I'll give you a few examples of how Apple's always visible UI and skeuomorphisms (that's a scary damn word) don't necessarily look as good as what you'd get in Metro, and doesn't necessarily offer any more function.
I'll use a cookbook app as an example here. Dunno why. I can't cook for ****. Think I've got a culinary learning disability. But since I was playing around with one in Windows 8, I thought it'd be a good compare/contrast. Specially since the Cook Book app is one of the best uses of Metro I've seen.
First, we'll use some cookbook app on the iPad. Forgot what it's called. I just found the pic on Google.
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It's skeuomorphic (still a scary damn word) as hell, and not exactly the prettiest example I could've come up with, but it's still a pretty good example of what I'm trying to go for. Anyone can look at it and say "hey, I know exactly what I need to do because of this and this and this are all right here". It's a little cramped, but it's easy to use.
Same thing with this, which follows the more traditional iPad UI.
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You've got that big bar across the top. All the buttons are obvious. It's probably about as easy to use, even with that goofy menu along the left side.
iOS is rooted in more traditional UI designs. We're all pretty familiar with it by now. Skeuomorphism and headers might be a little ugly, but they work, and work well.
But then we have the potential new. Metro...or New Windows UI or whatever.
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In Metro, there's really no UI to speak of, and absolutely no skeuomorphism to be found (I'm really getting sick of that word by now). A lot of people say it's very digital, but that's not really true. I once read that it's very much like reading an old magazine, and thought that came pretty close to nailing how Metro feels. It's got similar columns and tabs and all that good stuff, organized all nice and neat. It's easy to follow, and guides the eye.
And UI? There's no static screen that represents what does what like iOS, but it uses symbols and positions to show you what can be manipulated.
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Barring those select few with severe brain damage, just about anyone can look at that screen and see which button brings you back to the previous page. It's kinda obvious. You can tell that there are more reviews to see on that column in the right due to how it fades out and extends below the rest of the text there on the bottom right. There are no static headers or set buttons, everything is suggested.
That's what makes Metro so nice in my opinion. You get all the information and functionality you need without anything getting in the way. To me, it's a (potentially) better tablet UI than iOS. Both are easily usable, but Metro flows better, looks better, feels better.
Or at least it does when it's done well.