This is one of the must have features on dota 2 game that has been missing ever since. Having health number being showed overhead enemy heroes is very critical, it shows the user the number of HP opponent heroes got and it gives them a great tool to let the player know if they cast certain abilities would the hero die or would it be waste and opponent gets away.
for example, it has happend many times where sniper ulti goes to waste by not knowing the exact opponents HP number and ulting the opponent and the opponent having to get away with 10 HP. This goes for also zeus ulti, bounty hunter Shuriken Toss skill and so many other heroes. Having this feature is critical and i hope to see it being added to the game.