No doubt, there are problems.
Like you'd want to be able to switch not only between programs with left swipe, but back to the Modern UI as well. You can't. You should be able to, because the new UI is what's used to access to lots of programs.
Also, the Modern UI IE is too simple compared to Desktop UI. Even compatibility is different. It's effectively a "Mobile OS". Of course maybe this is fixable when Chrome and Firefox decide to make a Modern UI version that's as capable as the desktop one.
It's not possible to close multiple applications at once with Modern UI. You gotta go close them one by one.
The rest are fine though. Things like how they represent icons and such are merely user preference, and something that can be overcome quickly if the OS is usable.