>> Comments are sent as they are written; you cannot "draft" comments. > How is that different from pull requests via emails? (Also, on the website itself the comments can be edited.)

With github PRs, notifications are sent as soon as you write your first comment; in systems like gerrit and rietveld (and email) they are not sent until the reviewer chooses to send them. This leads to either awkward interactions if you start replying to comments while the reviewer is still reviewing, or unresponsiveness if everyone introduces hysteresis to avoid this situation.

This is IMHO the biggest problem with Github PRs; I don't necessarily agree with the Go team's decision to abandon the PR system but on smaller projects I have pushed for rietveld over PRs for this reason.