If you compare the issues list layout in YouTrack 3 and 4 on (3 is on the left, 4 is on the right) then you can see that every issue line is now taking slightly more vertical space.
Google products had this kind of change recently but, luckily, there's a "Display Density" option in Gmail:
Personally, I'd love
to go back to more "compact" display density in YT 4. Will there be such an option?