I've only been to one(my dad's side) and it was a basically they rented this huge shelter for a day at a park and it was a big potluck. But there's only so much they could do. I have over 23 first cousins of all ages on that side so with second and third and parents and wives and kids and all that there was probably 200-300 people there. I was also like 8 so I don't really remember too much except wanting to leave basically the whole time.
On my mom's side every holiday is pretty much a family reunion but there's 20ish people at most so that's a lot more chill with the younger kids doing whatever somewhere in the house and everybody else drinking and chatting.