One of my most important metrics when judging the health of a project is maintainer responsiveness:

* how long does it take for issues to have responses from a maintainer. this does not necessarily mean time to fix but time to recognition.

* Basically the same for pull requests: how long until PRs are reviewed or commented on by a maintainer and how valuable the feedback is. The kind of response can be all kinds of things like "sorry we won't do this", "please address these problems", etc.