I'm hating the absolute shit out of the Attack of Opportunity rules (or lack thereof).
Huh? Lack of AoO rules? They seem pretty straightforward to me...
Leave adjacency to a hostile creature -> they can use a Reaction to take an Attack of Opportunity with a melee weapon. You can use Disengage as an action to avoid the AoO. No reaction action left this turn? No AoO for you.
I mean, that's pretty much all there is to it. What's so hated about it, exactly?
EDIT: Also, apologies, I didn't peep the original linked video - I thought were were looking at Professor DMs "zone combat" via his "ultimate dungeon terrain" stuff he keeps pushing (which also uses distance zones), which has the issues regarding multiple enemies I identified above. I am unfamiliar with any other form of "zone combat", but I'll check some out now.
EDIT2: Read the Sly Flourish article. Not my cup of tea. Seems like it's making a bunch of extra work and rule changes for little comparative payoff... but then, I guess I've never really had problems running large areas before.
My approach is to have multiple battle boards represent multiple areas; I can segment a huge area as much as I want with those, and TotM the distances between them easily enough. (
"Miranda is fighting the goblin lord on this hilltop over here on this board, Cut-throat Bill is 200' due East up in tree taking aim, 100' South of that tree are Shelwyn and Norda simultaneously approaching the chieftain's hut on this board here..."etc.)
That way, I don't have to skirt all the inconvenient "edge cases" (as Sly calls them), for the sole benefit of not "losing the sense of wonder and excitement when we fall into the minutia of the mechanics" (as Sly puts it).
Your mileage may vary.