should refuse to stage/submit when other reviews came in meanwhile

it is somewhat common that while somebody has a review open, somebody else does a review at the same time. the other reviewer may give a -1, but the current reviewer may still give +2 and immediately stage the change without ever noticing the other reviewer's objections.

in such cases gerrit should display some kind of "in-flight collision" message like bugzilla does.
i think a straight-forward solution would be posting the comment and review score, but refusing to stage/submit if any other comments were added meanwhile.
clicking the submit button on the review page itself should obviously trigger the same error.