Ultimately the problem with these major ET eventlines is you can just walk away, not care about what happens, and everything will still turn out fine. It makes it really hard to care after the first one or two you get involved in. The disconnect between the actual stakes and the portrayed stakes is just too big.
But at the same time, the ET can't just nuke a nation or they'll piss off half the server. Even if they have a plan of nuking every nation Aegis Undead style, the nation that loses out first won't be happy.
I thought the Westerlands was a good balance for this. Maybe it was different from an ET perspective, but for me it seemed like everyone, resident or visitor, was there to fight the undead hordes, and so the ET didn't have to pull their punches nearly as much as usual. People were expecting, and wanted, to be constantly harassed with attacks, to wake up and see a village burnt to the ground.
The North of Aegis was a similar concept. For the first few months of the map, the Undead stayed almost exclusively there. You could easily wake up to your town being destroyed, but (1) that depended on player action and (2) you were most likely in the North just so you could fight the Undead anyway, so you rolled with it.
I think we had similar stuff in Anthos (and even last map? I dunno I ignored the Inferi), but that felt wasted because you weren't hearing of nearby player settlements being destroyed, nor was there any chance for players to destroy outposts of the antag, except when it'd happen all at once as part of a scripted event. Again it just felt like something that could be totally ignored.
Moving on, the climax:
Done well: Aegis Undead, Anthos Harbingers.
The Undead story culminated in nations capitals falling one after another like dominos, with major political upheaval as countries collapsed or capitals moved to other, safer towns. You had literal refugees and the world really felt like it was collapsing. Cool time.
The Harbingers were totally different. They didn't didn't destroy nearly as much (although they did kill a couple notable cities); Anthos just kinda got deleted once we got the Fringe because of performance and we were bored of it. But we did get to literally invade Hell, and that was really cool. What was nice about it though again was the dynamism. You had these mob-spawners sending waves of mobs at you, so you'd push them back and quickly erect a stone wall to keep the ground you'd won. Recover and charge over it, destroy some mob-spawners, build a new forward outpost. It was nice determining our own progress.
Both of them had their own apocalyptic ends. Next time I'd like both tbh. Have the Antag start off in the "danger zone" of the map destroying shit there, and towards the end they bust out and start destroying player regions, nation capitals, like nobody's business. Do attacks with very little warning, maybe attack multiple settlements at once to spread the forces thin. And then when it comes down to the final conclusion as the world burns, we invade some shit to kill them off. But oh RIP, our map has been tainted and destroyed by evil forces, nothing will grow here any more, on to the next map. The end.
The Inferi did kinda have an "invade Hell" ending, and it was a nice event over-all, but unlike the Undead or the Harbringers, they never really busted out of their corner of the map so they always felt totally irrelevant to me. And the final event was cool, but ultimately it felt overly dramatised for what you actually felt and experienced as a player. You had no hordes rush you in PVE, you didn't have famous settlements get wiped away across the map, and unless you were from that shitty little island they were on, you probably didn't really care or notice that it fell. It was this huge big world-ending, uh, ending to an antagonist that felt anything but world-ending. I mean there were even player wars going on right in the middle of it; that's how little people really cared. Also, having an antag like that not be the map-ending event feels really anti-climactic.
And one last thing I touched on there: Have PVE ffs. The best parts of the Westerlands event lines were sweating like a madman as you fought horde after horde of mobs, seeing your friend on half a heart and rushing in to save him, before just barely escaping yourself. Seeing others pop around you, your numbers dwindling while the hordes never stopped coming. The Undead and the Harbringers too had lots of really fun PVE events. Sure CRP events are cool sometimes, but can we mix up the endless walls of text with mechanics for once? This *is* Minecraft.