I'm not sure if this has already been suggested or not, but I would like to suggest that OOO implement a monster health bar system, where the monsters have that little bar of health above their heads. I suggest this simply beacuse I believe it gives the player a better indication of how much dmg they are doing to the monster, and how much more/less time they will need to spend fighting the monster. This will help players to form better strategies when vsing strong/weak monsters.

And for those players who don't like that little bar, maybe it could be like the damage indicator, and have the option of being turned on or off.