Could these event by any chance be triggered by certain conditions? For example;
Last raid was X amount of days ago (I’d say once per week to avoid the novelty wearing off. The music in Boundless is superb, but you made a wise choice to have it play after long intervals; it makes the moment seem that bit more special - I feel these events should be treated similarly)
X amount of players within a certain proximity of one another. It would be a shame to have the weekly raid happen when there’s nobody around.
Settlement Prestige rating (or classification) is above X. The scale of the raid could depend on the size of the settlement. I can see it now - Great Cities having shelters, keeps, towers and walls in place in preparation for such events!
These mob swarms were so much fun. Even though they were technically an exploit, I believe most of us weren’t there for the experience or loot (although nice), we were there for the action and comradery.
One more suggestion;
- Bosses - have the raid culminate in a battle against a tough opponent. Perhaps even have themed waves followed by a named opponent, for example; a thousand Spitter’s follow by their fierce and terrifying leader ‘Pseudo’s Bane’!
Edit; another suggestion;
- Changes in weather and music. @Scratchnwiff made a comment about Helms Deep in his video which got me thinking; wouldn’t it be ominous if the music took a sudden turn and atmosphere began to change?
I don’t know if you’ve played Kingdom, but during certain nights the sky goes blood red, and eerie music begins to play before the onslaught. I think that game captured the dread of swarming raids perfectly.