The desktop has remained mostly unchanged, however you'll notice that there are Metro apps pinned to the start menu by default. So it seems that both the classic and "Modern" UIs are now slowly becoming combined. Not that they should have been separate in the first place.

Unfortunately, the built-in screenshot mechanism won't let me take a screenshot of it, but Metro apps now have a title bar.

Again, the MS shills are touting this as some big game new feature. It's not, and all it really serves to do is prove Microsoft made yet another incorrect assumption about the marketplace, and to invalidate more existing documentation.
I'm not quite sure why, but it is still not possible to display these applications in windows. Despite the operating system being called "Windows".

One thing I'd like to point out as well: it's possible to "close" Metro apps now, but this doesn't really close them, all it does is drop it into a "sleep" state. Found this out the hard way while trying to remove files that were still "open" in Reader...despite Reader being nowhere to be found! Another bug, as far as I'm concerned.

Notice that the about page makes no mention of this being Update 1, which suggests that very little backend work was done. I thought that was the point of service packs, was to do backend updates?

The ribbon UI is still as stupid as ever.

Shutting down Windows 8.1 Update 1.