At least Gruber is rightfully giving props to Microsoft for the very original UI. Every time I see anything Metro based I'm struck at what a breath of fresh air it is in mobile.
The Metro "Theme" which is attractive but I wouldn't call it mind blowing. It basically plays off a trend that had been developing since the web gained prominence which is to ditch the pseudo-3d interfaces for a flatter look. Again, I don't deny its attractive.
The Interface Elements - As far as the UI Metro doesn't change much. It basically boils down to Widgets instead of icons. I mean, Android already had desktop widgets. Again not saying what Microsoft is doing is bad (it isn't) but is it really "a breath of fresh air"?
The real innovation of Metro in Windows Phone 7 is the wall concept where people can scroll in every direction. But that doesn't seem to be present in Windows 8.
It's refreshing because it is, simply put, different. Android and iOS much more closely resemble each other than either resembles any recent Windows phone OS.
That's my take, anyway.
http://images.yourdictionary.com/images/computer/_PROGMAN.GI...
That is why Metro is such a breath of fresh air. If it came from Apple everyone here would be praising Apple for breaking the status quo, being the UI disruptor, etc. etc.
EDIT: By "tweaks" I mean "under the hood", as far as I can tell.