Lots of these things are changed or fixed/tweaked in 8.1. Boot to desktop, options to tweak the start screen so instead of the tiles you get the app list. Options to sort the app list into more of how it was in the start menu, and if anything you now see more apps listed of course. Tweaks to snap for metro, they just need to make it so metro and desktop win32 apps can snap side by side in a better way. The sharing of the desktop background on the start screen helps visually, and will help people new to it, as with the return of the start button since that's one less "hidden" UI element. Still think the charms bar should get the option for a visual UI element as well, so desktop users can click on something to bring It up, but that's not much of an issue really. By adding search buttons into the core apps with 8.1 users will see and get used to the new slide out charms menu. New unified search in 8.1 also covers early complaints from 8.0 users.
New tile sizes are good as well, I'd like to see them improve the larger/extra large tiles more, right now you just see more info displayed but I think they can/should actually turn the tile into more of a widget when set into this new extra large size. There's room for the tile to have controls in it this way.
A future notification center will be nice, also have it incorporate the desktop systray into it, it'd be a slide out window like the others so it fits with the new UI, that way the old tray icons would be at the bottom while you'd have a list of notifications for the rest of it.
One last thing they could do is find a good way to expand the taskbar so it supports metro apps as well, having it show up in metro would be a bit odd though as the space below is taken up by the app bars but it could be possible with some more thinking. In the end the goal would be the merge the two UIs more into one.