Upgraded to Windows 10 today. First thing I do? Claim my free copy of Minecraft: Win10 Edition.
Controls are slightly clunky still - when playing with mouse + keyboard, mouse sensitivity is too high when moving around, then suddenly too low when in a menu.
Interface needs work - menus vary from ones specifically designed for the PC edition (like the classic Inventory screen) to ones designed for touch control (most everything else). Mouse and keyboard aren't as fluid on the ones designed for touch control as they are on the Java version, and Xbox controller is clunky and unwieldy in every menu. There should be an option to choose your interface based on control scheme.
Block placement is really bad in regards to partial blocks. In the Java edition, when placing blocks through partial blocks (torches, grass, etc), those blocks only get in the way if the actual torches or grass come between your cursor and the block you're aiming at. In Win10 Edition, if the 1-meter block space containing the torch or grass gets in the way, the block you're trying to place WILL be misplaced.
It's a decent start, but definitely still needs work.