Quite often, I leave a comment on new answers if they add nothing to existing answers. Sometimes I also downvote because of this. I also think this is a quite important thing to do when reviewing.
But this can be quite tedious to do, because to compare, you need to go back and forth between the tabs "Answer" and "Other answers". The solution I'm currently using is to open a new window so that I can have both the review answer and another answer on the screen at the same time.
I suggest the possibility to view them side by side. Or the review answer above the others, but always in view when scrolling through the others. I'm not a UI guy, so I leave the exact details to someone who knows better.
This also applies to the case when looking at the "Question" tab to see if the answer really answers the question, but in this case, I don't find it equally important, but maybe it could be solved at the same time.
EDIT:
As mentioned in comments, this also applies to the late answer queue and the low quality answer queue. Thanks @Elikill58 and @Tomerikoo