I enjoy the height advantage system. As its a variant rule its indisputably fair game and not an exploit.
I am most interested in being placed in a situation where it is - or can possibly be used against us. Where a superior force in number but not level has the high ground and we have to try to close the distance or fight at disadvantage from range.
This forces players to utilize spells such as Fog Cloud and Arrows of Darkness, or later spells like Wall of Stone (which your caster would have to stay behind to maintain concentration but could pop out of to launch spells at the enemy and then return).
I would like to see more use by NPCs of tactics that do provide cover and concealment to ground-based enemies. When you have low-level wizards, Booyahs and whatnot they should all be able to cast Fog Cloud and do so when someone has Advantage and is using it. Or use the Blind spell properly.
The problem is that I can't find anywhere in optional variants that High Ground grants Advantage. But, I do see many DMs give Cover and some flat bonus to hit.
There is an variant that Flanking (basically if one character is threatened and another comes up, both characters gain Advantage) gives Advantage but I don't see many DMs using this as this is more to 3E and 3.5E.