When you give a mob the final swing, then these colored clouds puff up in the color of the enemy type. They hide the physical reaction of the mob’s rag doll to the last incoming blow.
In the super repetitive static quests where you’re mostly only killing mobs, I see my last attack in my playful mind as a finishing move.
This is actually a great motivation in this static progression; To have fun with the combat (and for many of us you lowered the quality so much by removing stagger and making the combat look like these discos parties, some players do in the cities… ).
Also earlier gameplay footage from this “call to arms video” didn’t have these overdriven colored visual effects that kill the immersion especially much, when there are many players around. This is a firework! Actually, I only got attracted to the game by this dev video (call to arms) and last year’s game preview.
Also for my girlfriend many aspects of the game changed to the negative since then…
So, please bring up an option in the settings to disable these disturbing colored clouds that hide the action in general and especially a well animated physics based reaction of the mobs that give you the responsive feeling of impact and hit feedback; the responsiveness and impact that is much gone from for instance the heavy attacks, where the mob just stands there without a reaction and any response losing his blood 
;
Sometimes when the game had performance problems in the beta, these effects didn’t appear, which was cool but which probably was a bug or not meant be; but we loved it!
This really should be brought up, since it is a super small change that takes no effort but brings a huge outcome for many players, who are not into these super colored WoW games…