Honestly the only good wiki I've ever seen is Wikipedia, and that's only because Google exists. Wikis suffer from the most ridiculous discoverability problems. Unless you can successfully guess a page's title, find it on Google, or the wiki has good searching (many don't), I find myself clicking around random pages to see where to start.

Especially when I am dumped into a random wiki for the first time. Starting off in Minecraft years ago, people said "read the wiki first!" with no link to the first page I should read, or any successive pages. Completely useless.

Maybe I'm missing a nice table of contents that every wiki secretly has hidden away, but tables of content exist for a reason. Discoverability.