Yes, most people are just focusing on how flat dock is, dull yosemite looks etc, I don't like it either but the issue is readability and contrast with respect to background (easy on eye). Issue is not only the font-size, they made a big mistake by making it thin. They made it with iOS, may people gave bad feedback about readability, then added a feature "bold", but same mistake here in yosemite. There is a feature in the Accessibility option to increase contrast and reduce transparency, these help but still not as good as before. Thus I use my macbook pro retina with mavericks with best for retina option, but iMac retina with lower resolution. I suggest you all (since apple does not allow me to show you the link), tekrevue site (or any site you find), where article title is the new icons of os x yosemite-a-side-by-side comparison, now just focus on (not flatness) but 1. activity monitor icon, 2. calculator, 3.calendar icons.
1. activity monitor, it shows that thy chose "thin" line as graph, this is a problem when there is a plotting something, it will be hard on eye when that plot is small (no problem when things are big like this icon, however nothing is like power point presentation, we read pdf papers or write articles)
2. calculator: the font and numbers are thicker, easier to read. 3d also gives additional easiness on eye but I won't touch on this, if Apple chose flatness, fine. But look at the color also, create terrible contrast. In high school if you take a drawing/painting class and make a painting, the first thing you learn is: make background "dull or pastel-like" color to bring the main item frontside on eye better. By choosing hot colors like folder color hot red or calculator color like this, then you create distraction and eye strain. Weirdness enough apple and (microsoft) is going in the direction of reducing color like side bars in finder "to reduce the distraction etc", became a fashion, but in reality it becomes now harder on eye in desktop management.
3. The calendar icon, this is striking, and shows my point clearly, I suggest you find in google anywhere these comparisons, left previous version, has 3d effect, right yosemite version 2d flat. Again lets say flatness is OK, but look at font thickness and darkness level. This is the exactly the issue people are having when reading smaller fonts than this of course. It will be very helpful when you use fat fonts and darker fonts, then you don't need to change monitor color/contrast settings. Now on my iMac retina with yosemite, everyday I am trying to change setting since after 3 hours in front of pdf reading I feel strain on my eye. Apple followed Microsoft on this and made a big mistake with respect to font and color scheme. Again the problem is not Helvetica vs Lucida (partial issue), but also font thickness and darkness, color schemes on the desktop environment. What do I mean by color scheme, even finder previously was better on light blue compared to gray. Now I have to put increase contrast, then finder background with stripes became very dark gray, background is more visible compared to main object texts. Again the idea is to make the background lighter, the main objects darker. Whoever designed the OS X before was perfectly know what he/she was doing. New guys really don't know about this, such a mistake is unacceptable.