This has been up for debate on other tbc forums in the past. But as tbc works right now you can see your enemy targets hp in % in an accurate manner but NOT in a numeric value. You can bypass this by downloading an addon called MobaHealth or something of that kind but its data is not always (if ever) accurate. This can however be implamented. The question is will you as it's not strictly "blizz-like", then again neither is x5.
Leave your thoughts down below.
Cheers.

