Thanks very much for the detailed comments and examples, guys—very useful feedback!
A lot of it conflicts with what I've heard from other readers, but a lot of it rings true so I am making a few adjustments to the styling as we speak. I'll probably push them out later today.
Any typesetting job on the web is a dance of compromises, and I erred on the side of accessibility—I'd rather make people scroll than squint. Some of this stuff comes down to preference, too.
In any case, I appreciate the feedback and will implement aspects of it today.