New features are great, but I wish they'd make more of an investment in improving their core code review functionality. The lack of an "interdiff" view (between revisions of a PR) and the lack of a proper way to mark PRs as dependent on one another really limit the utility compared to other code review platforms (thinking specifically of Gerrit and Phabricator/Differential here).
When you've left a review, you also generally get a “View Changes” button in the conversation that takes you to the changes since you last viewed, if new changes are pushed. The issue with this particular link is it tends to be ephemeral.