eTargetList is an addon that displays a list of units around you as HP bars.

displays a list of units around you as HP bars.
each bars have text that shows level, name and HP(%).
there are indicators that show your current aggro.
you can choose your target through this bars and can start attack.
you can choose unit that matches various conditions in the list by macro interface.
addon manager support

after installation of this addon, GUI configuration window will popup on your screen(see screenshots).
set your configuration and close, then this addon starts working.
you need to check the following in-game option
[Interface Settings] -> [Health Bar] -> [Show Health Bars] and [Enemy Health Bar].
display distance goes along with this setting.

despite inside of displaying distance, if the units are too tall or behind you the bars would not be shown.