Time-to-review is a good metric, although as with many metrics, it is possible for it to be gamed, and it can be context-sensitive (Mozilla and Stripe probably

Time-to-review is a good metric, although as with many metrics, it is possible for it to be gamed, and it can be context-sensitive (Mozilla and Stripe probably have various other team and cultural differences). That said, no-one (including collective engineering organizations) should enjoy the sense that potentially useful code changes are piling up unreviewed.