I wouldn't mind some sort of optional overlay, doesn't hurt the game in any way. I'm one of those people who "still" think that Agro indicator and telling people the mobs level by default is LAME.

Seriously implement a bestiary and make them earn that information! If your too lazy to get the bestiary page, google it! I wouldn't mind the indicators being available after you got the beastiary info though.

/off tangent rant.