Windows Phone App UI Issue
I know that developers aren't required to follow the stock WP app UI, though most do just because it's easier. I love the WP aesthetic, and I've been a Zune owner since it's first release, so I have no qualms about Metro (or whatever). The only issue that I have with apps on WP is the layout of the UI.
As you can see, half of the screen is given to just the title of the app and the sub-menu you've chosen to be in. This leaves just half of the screen for actual data. Maybe this isn't such an issue, and it's not turning me away from buying a WP device, but it is definitely something I am keeping in mind when downloading apps. I want to actually see the content of the app, not just it's title and sub-menus.