For me, in typography the four most important things are these, in this order:
- appropriate choice of content/mono/headline typeface to the usage (regular content / preformatted content / headlines); that's really easy;
- spacing settings: line height, character horizontal spacing; that's also easy, though there's much more room for nuances;
- vertical rhythm, that's a big one; when wrong it's not as destructive to readability as what I mentioned above, but it feels really wrong, i.e. you're not sure why, but you just want to leave the site. Vertical rhythm is very hard due to technical reasons, and it's nuanced as well;
- and, finally, in the last place for me, the typeface choice. I find the differences between various fonts of the same type to have, by comparison to the things mentioned above, the least influence on my experience, whether in the aesthetic or functional sense. Not that I'm not sensitive to differences between typefaces, it's just that those other things seem to be much more influential.
- appropriate choice of content/mono/headline typeface to the usage (regular content / preformatted content / headlines); that's really easy;
- spacing settings: line height, character horizontal spacing; that's also easy, though there's much more room for nuances;
- vertical rhythm, that's a big one; when wrong it's not as destructive to readability as what I mentioned above, but it feels really wrong, i.e. you're not sure why, but you just want to leave the site. Vertical rhythm is very hard due to technical reasons, and it's nuanced as well;
- and, finally, in the last place for me, the typeface choice. I find the differences between various fonts of the same type to have, by comparison to the things mentioned above, the least influence on my experience, whether in the aesthetic or functional sense. Not that I'm not sensitive to differences between typefaces, it's just that those other things seem to be much more influential.
I'd like to hear others' accounts of this.