We had a go at Phabricator for code review. Suddenly, there were two opposing camps - those who hated it utterly and those who loved it and wanted to tweak the heck out of it.

Fortunately (for my team at the time, which was very resource constrained) those who hated it eventually won, but I, being kind of on the fence regarding it (wasn't keen on the UX, but liked the features), sort of wondered what would happen if someone improved the UX beyond the tipping point.