From spring and summer 2016:
Certainly awful compared to Discourse 
IMHO.
+1
Are there other, more recent and/or substantial case studies?
Constructive criticisms?
Food for thought
Not all related to Discourse …
… we now have a Discourse instance online for you to find help installing/configuring mailcow!
We can finally stop using Github as our forum and keep using it for real issues and bugs.
Github issues are not made for this type of discussion, you should only use github for discussion on code and implementation or problems, the forums should be used otherwise
… we try not to use GitHub for discussion. I think we have all the information we need in this issue, if you’d like to continue discussion please see the online forums. Thanks!
GitHub is not a discussion forum, it literally is one of the worst platforms you can choose for that. …
T11268 integration with discourse forums – Phabricator (closed, wontfix):
From a usability perspective, I find the forum software discourse a lot better for discussions …
Why you must not ask questions on Github issues – Medium (2016-08-09)
Two-way sync GitHub issue tracker - As seen on issuepress.co
Last but not least (this topic should not be an exercise in bashing GitHub): Suggestion: Introduce a Discussion tab · Issue #44 · dear-github/dear-github