Comment by tardyp

Ability to review diff between two versions of PR is a great missing feature in GitHub. When dealing with large changes, GitLab review flow is IMHO easier for reviewer. Gitlab store each push of a MR branch as different version (as hidden refs), which make the feature possible. In GH, you force push a branch, you loose the old code for good, so reviewer has to remember why he did that comment before to see if it is still relevant.