[justinph]

You're right, Helvetica is and was a poor choice for Yosemite, even if you have a retina screen. It's not a screen font. Lucida Grande was a great screen font, but the boldness of it worked much better on 1x screens. With the added fidelity of retina screens, it just looks too strong. Apple probably should let you choose or choose for you depending on your pixel density, but that's not their style and they've always been willing to make compromises in choices for the sake of forward progress.

San Francisco as a system font in OS X on a retina screen is very good, even if the current hacked implementation has it's quirks. The thinner stroke intersections are somewhat reminiscent of ink traps. I'm not certain, but I'd be willing to bet it has to do with sub-pixel anti-aliasing and not making the stroke intersections look too heavy. To my eye, the taller but symmetrical bowls look really good and help keep an even cadence between all the vertical forms. The wide range of weights is also really useful. Maybe Apple will put that to use in 10.11 for retina and non-retina screens.