With Photoshop CC 2014 Adobe introduced the stupidest “feature” Adobe has ever introduced. (And that’s saying something!)
From now on Photoshop uses Microsoft’s Windows Ink API, which simply doesn’t work. There are odd circles appearing around your cursor, right click doesn’t work reliable and pressing alt (to pick a color for example) takes ages to temporary switch the tool. Luckily it is possible to disable this Windows Ink thing.
In your Wacom Tablet Properties go to the Mapping tab and there you can uncheck Use Windows Ink. Now everything works just as in the old days, but since Photoshop CC 2014 (or newer) relies on Windows Ink, pressure sensitivity won’t work after disabling it.
But luckily we can switch back to the old so-called WinTab functionality. Create a text document called PSUserConfig.txt and insert:
# Use WinTab UseSystemStylus 0
now save it to (you can just copy and paste it in windows explorer, it will automatically redirect to your current user directory):
C:\Users\%USERNAME%\AppData\Roaming\Adobe\Adobe Photoshop CC 2015\Adobe Photoshop CC 2015 Settings
Restart Photoshop and now everything should work again :) Thanks to M Shaw for providing this solution!