I don't actually use good reads, but I clicked around - everything I clicked on loaded faster (less than 2 seconds, usually less than 1) than everything I clicked on in medium (always more than 2 seconds, where this blog post is hosted).

Neither site is fast, but "one of the slowest around" doesn't track either.

I think it may be more so for logged in users. When logged in, and I go to the homepage, which is essentially an activity feed, it has 93 requests, 4.4MB of resources (1.5MB transferred), and took 7.66 seconds to finish.

In my experience, Goodreads loads slower on a phone than on a desktop browser (and it's only the initial load that I notice being slow). I've long suspected (without evidence) that this is intentional because they nerf the mobile web experience in an attempt to get you to use their app.

I don't use their mobile site, but the android app works really well, and looks great.