I know a lot of people don't mind Helvetica Neue system wide and are happy, but it's seriously a legibility issue for me and others with non-retinas, and some retina displays and the resultant effect is eye strain. The font isn't crisp, it's too thin, light, and cloudy, at times blurry, and too small in the menus and apps like Safari and Mail which makes it hard to read (even after changing all potential settings to increase contrast).
I'm really hoping that Apple addresses this font legibility issue with this release and allows for a choice to have Lucinda Grande system wide for non-retina displays. I really miss the crisp clear darker font of Mavericks for functionality. I'm not feeling very confident that this will happen with this release though.