This thread is almost a month old and Win10 is still the same fractured OS it was then. Some of the main problems
The UI is cobbled together, at the core it's the Chicago interface which began in Windows 95 flattened out, it has elements from Windows Vista notably the Ribbon, the back again start menu is an evolution of the dual pane introduced in Windows XP and with Metro/Modern tiles included (really this is just to make it look like a shrunk down start screen which you can choose to thow back to full screen as "tablet friendly"), finally the UI controls are thrown in as Modern/Metro look but all appear smaller and less spaced and really aren't as touch friendly.
What they really should have done is bring in more functionality to the Windows 8 interface and allow it to run windowed (which Stardock already offered) rather than the poor attempt at craming touch apps into the 20 year old interface.
Example
The UI is damned bland! The greatest example of this is the new browser they could have code named it "10 shades of grey". It's just completely boring to look at. As usual the Windows team need to catch some inspiration from the Office team which is where all the talent seems to go, and snap some colours in, I'm not simply referring to title bars and task bar.
Here's a more uniform approach that's less dreary.
The desktop presents three different icon types, wireframe, Modern/Metro and legacy (desktop). Atleast the color backgrounds of the Modern icons bring in some badly needed color! They also made some damn strange simple changes like why the hell are avatars circular when other UI elements (notably tiles) are square? When the login screen, the first interaction the user has looks out of place it's a problem.
For those saying "IT'S NOT EVEN IN BETA YET" I'm sorry but WAKE UP! It should be obvious the Alpha, Beta, RC1/2, RTM approach is out the window given MS have opened evaluation up to anyone interested. They are 50 days out from the final product, you're not going to be seeing any mind blowing UI changes unless all the senior designers are due back from a six month vacation!
While Windows 10 will be a success for MS (in the same fashion Apple spin every product release as their best ever) due to the free dump to every legit user. It's also going to be a gold mine for mobile PC techs who are scraping it off home users PC's and for companies like Stardock and Yamicsoft (Windows x Manager) who will no doubt find ways of making it a far more usable and interesting OS. Maybe in 12 months time the problems will be so apparent that a '.1' major update is applied, Just as Windows 8's update addressed desktop problems Windows 10's update will be "damn we dropped the ball on touch interfaces".