are you using your graphics unscaled? if so try adding any sprite at 2 or 4 times the size you want to use it in game, for example if it should be 100px in the game, the imported graphic should be 400px and then scaled down to 100px in the editor. hope that helps!
I'm scaling the graphics to a size that I feel fit the scenario, it is asset resolution is often a bit bigger, not 4x bigger, but it could be 1.2x - 1.5x the native resolution scale. To me, creating 2x or higher resolution assets would be an enormous waste of resources. (it would require excessive use of graphic memory or RAM)
The problem is that it actually scale nice on browsers on PC. On mobiles however it looks terrible, It seems as if it has to do with the device pixel ratio (something that is determined in the browser in order to give better web experience viewing text on high ppi displays) I made a comparison, you can clearly see the reduced pixel quality on my LG G3 compared to the PC
Any suggestions anyone? or is the pixel ratio corrected once exporting it as a native app?