I'm an aging developer primarily based on the Microsoft stack, and this is disasterous IMO.
Others have pointed out the horrendous looking "tiles" on the home page, the disfunctional touch screen, the painfully slow transition animations, the absurdly large fonts on a small screen, and bizarre partial glimpses of neighbouring screens (again wasting precious space).
The iPhone was released how many years ago? I reluctantly bought one, and iTunes is as bad as the notoriously bad QuickTime, but the device itself is functional and fun to use!
Microsoft is missing the boat on portable devices. There is a space between closed Apple and open Android. Disappointed that no-one seems willing to fill it.