Is there an issue with the fonts in OX 10?
It appears the system font has changed to the reported "San Francisco" font. At present, a HUGE step backward in readability, particularily on non-Retina displays. Helvectica Neue was the system font in Yosemite and was much clearer in the public release. The new font is smaller, blurred, and difficult on older eyes.
There were a bunch of additional Helvetica's installed. I was getting a Greek version replacing the stadard Helvetica. I removed all the errant variants.
The font change isn't something I like to see either. I can see just fine, even the new font, but it doesn't look very nice to my eyes... I've heard the San Francisco font was designed to be easier to read on tiny screens such as the Apple Watch than Helvetica Neue, but I greatly prefer Helvetica Neue to the new San Francisco font. I'm glad to see I'm not alone in this opinion.