I've found really simple solution for users who using windows dpi scaling and struggling with problem "everything looks bigger in Opera 24"
- Go to opera settings - web-sites.
- Change "Page scaling" from 100% to 75% (if you are using 150% and above dpi scaling in Windows) - or use ctrl + mouse wheel to find your specific percentage - you'll see that is your scale when all pictures on site became clearly visible, not blured.
- Adjust the size of your fonts in fonts settings.
Of course it is temporary soluiton, but at least it works - now everything in Opera looks clear and smooth.