You can opt out of this on a per-app basis (right click app icon, Compatibility tab, select "Disable display scaling on high DPI settings") and have them just display everything really tiny if you prefer that. This is actually a decent option if the app has its own scaling but doesn't properly interact with Windows to enable it. I still run Sublime Text 2 and have it set to disable High DPI scaling and then just use a bigger font point size to make the text readable; also used to do the same with Chrome back before it had proper High DPI scaling on Windows (disabled DPI scaling, then just used the normal web page render scaling).
It also looks a mess, mainly the random font sizes, but also the fact that they've tried to modernise everything, like menus, etc. (that they clearly didn't get around to with W8), but there's still aspects that have been forgotten and are in the W7 style. So there's W7+W8+W10 all in one. I didn't mind so much with W8 because 'modern' was 'over there', and W7 with some flat tweaks is 'over here'. But now it's all thrown together. Not pretty.
Then when it would only randomly 'see' certain domains on my work VPN, and just be blind to others, I'd had enough... and bailed. I've never bailed on an OS before, always given it a chance to settle in. W10 just doesn't feel finished.
That's a consequence of the cheats that MS did a long time ago in how they render TrueType. The short version: instead of properly kerning the rendering, each glyph's x-location is rounded up to the next pixel boundary, causing nasty misalignments (some of which accumulate over the line).
The long (but very interesting version: http://www.antigrain.com/research/font_rasterization/index.h...