Windows 10 build 10240 auto update landed on my laptop just there, and so far stability is greatly improved. In particular, calc (the Windows Calculator) no longer crashes on load, and I use calc surprisingly frequently, partially for the company accounts, partially during programming.
Unfortunately, the calc in Win10 is a Metro thing which requires you to be logged into Microsoft Store. I prefer local accounts so I am NOT permanently logged into Microsoft, and therefore calc won't work. Solution: install Win8.1 calc on Win10: http://winaero.com/blog/get-calculator-from-windows-8-and-windows-7-in-windows-10/
Win10's not great start menu is good enough I haven't felt the need to install Classic Shell (which restores the Win7 start menu) which is good - just remember to always right click the Start button now instead to get an actually useful Start menu! But it's stuff like launching calc requiring you to be logged into Microsoft which pisses people off. Windows 7 had polish ... there was really very little reconfig from the defaults one had to do after a fresh install past updates. I really wish Microsoft would "get" this already ... shipping Windows with a working calculator app was something you could take for granted since Win3.1 days :(