Hello,
I've been testing Plasma 5 for some time, and although I think it is a huge step up from Plasma 4, one thing I am still not totally satisfied with is the font rendering.
The usual fonts like DejaVu Sans Mono and Droid sans look decent enough with the standard Fonts setting tweak(Fonts -> Configure -> RGB, Slight), but window titles and texts in Plasma apps that use Oxygen Sans look blurry and hard to read, so I guess the rendering of Oxygen Sans is the culprit here.
The font looks really beautiful when is drawn in-your-face huge, but when it's rendered at normal 10-12pt its quality seems to downgrade

Then just now I've come across the new 5.2 beta release article, and figured out the font rendering shown in the webpage's screenshot( https://www.kde.org/announcements/plasma-5.2/full-screen.png ) was a lot clearer and more readable.
Can anyone please point out a way how to reach this same rendering quality? I am not using any Infinality patch, just the standard slight hinting, lcddefault filter, RGB subpixel rendering and 96 dpi.
This is how the font rendering looks like in my monitor: http://imgur.com/BoaGwzW.png
Thanks!

I guess, I might have had the same issue. You could go and try forcing the font-DPI setting to a specific value (e.g. 96). This helped me. Also the wallpaper was blurry, just like yours