Pathfinder’s The Emerald Spire is a true megadungeon. Rise of the Runelords was a campaign, but Emerald Spire is an big old fashioned dungeon that just keeps on going and going. I like boutique, meticulously DM-crafted worldbuilding. I like open, sandbox games in unique homebrew settings. I also really like giant, out of the box, hardcore superdungeons. There is no need to be forced into some “new school versus old school” rivalry here. Have some cake. Eat it, too! Then throw it at opponents for d3 non-lethal damage in a giant food fight, that’s what I’m saying.
If you have talked to me at any length in the past year, you’ve probably heard me go off on a rant about defeating The Temple of Elemental Evil; one of the perks of playing one of the great classic dungeons is that you can brag about it, as well as share war stories with other survivors. The Emerald Spire belongs up there with your Tombs of Horrors and Castle Ravenlofts; PCs are going to be delving into the Spire for a long time, and I’ve no doubt it will generate its same share of shaggy dog stories.