Drupal.org report card:
Style/look... A
Speed... C-
Structure/Navigation... C+
I find myself wishing page downloads at Drupal.org were faster. On my DSL connection it takes 2-5 seconds to download pages on this site. About the same on the DSL at work. That's not awful, but it's not very good for a site that's basically all text. Even for a dynamic site, I'd say that's too slow for my liking -- certainly nowhere near the speed of thought.
I'm hoping this is a problem with either the server on which this site resides, or the design of the site, and not a problem with Drupal (the CMS). I'm just starting to mess with Drupal and it looks promising, so I hope (lack of) speed doesn't end up being the deal-breaker.
As for structure/navigation, I don't like the audience-oriented (or role-oriented) navigation in the handbook because it's not possible for the site user to know (in most cases) which role they fit into -- I'm all of those things (user, admin, theme developer, etc). Nor is it always possible to know, when you're researching something, whether it fits into a particular role. I also don't like having to page through the lessons on each page to see what comes next -- especially when I have to scroll down for the "next" arrow. It's in the style of a tutorial, but I'd prefer a reference. Alphabetical or concept-oriented index/reference, vs. a narrative. Something more oriented toward vocabulary and concepts, rather than audience and narrative. By narrative I mean that there seems to be an expectation that users of the documentation will page through it in a linear way, learning as they go along. That's an assumption that will probably apply to very few users.