MartianCraft’s Nick Keppol wrote two incredibly detailed posts on the typographic strengths and weaknesses of Apple’s new sans-serif typeface. Part one looks at San Francisco in contrast with Lucida Grande, Helvetica Neue, and DIN. Part two focuses on San Francisco’s various weights, with particular interest paid to the nuances between San Francisco UI, Text, and Compact.
I have a non-Retina Macbook Pro, and the general legibility of OS X was dramatically increased after I upgraded to El Capitan. San Francisco is so good that apps still using Lucida Grande or Helvetica Neue stick out like a sore thumb.