* Clean design. No loud colors, animations, popups or clutter.
* Sensible CSS usage. Good colors, contrast, margins.
* Large text size. I don't know why so many sites (including HN) mess this up. I don't want to have to magnify a site 3-4x just to read the text from a reasonable distance.
* Rich content when needed (images, GIFs, video embeds), all serving to complement the writing rather than getting in the way.
* Reads very well on mobile devices.
* Loads quickly.
Sites like these are a perfect response to many different sides of the web design debate – including those who preach that plain HTML with six tags and no CSS/JS is the only acceptable answer for a functional website.