A different take on Mega-Modules . . .
What would I like to see?
Mega-adventures not in the sense of how many levels you go up, but in terms of depth, flexibility, and ease-of-use.
For instance, the adventure might be 96 pages that covers the same amount of territory as a typical 48-page module. But:
1. Instead of being usable over just a limited range of three levels (say, 4 to 6), it can be used at a wide range of levels (say, with a prime focus on 4 to 6, but usable at levels 1 to 10). All necessary adjustments for EL’s, CR’s, treasure, and DC’s are included (probably in appendixes), and notes on special considerations when used at various levels.
2. Include notes to create a “living world” effect. How do creatures and NPC’s react to various PC actions? How do they interrelate to one another? How do creatures react if surprised? If they have time to prepare? If the PC’s react and retreat? What about reinforcements? What about some NPCs which are not integral to the main plot, but with some interesting notes to still make them three dimensional?
3. Include notes to help the DM adjudicate a wide range of possible PC actions. Most adventures seem to assume the main PC tactic is to charge in with spells flying and swords swinging. What if the PCs attempt to gather information? (Any medium-to-high level module should explicitly deal with all the common info gathering methods available to PCs. Everything from scrying to Legend Lore to ethereal scouting). What if they attack from an unexpected direction (including passing through walls, teleport, etc.). What if they infiltrate the enemy ranks? Attempt a parley?
4. And finally, for the biggest request of them all: make all this information easy to use. Minimize having to flip to three different places to find what you need. When including a lot of details, prefix it with a quick-read summary. Pay attention to the proper use of layout of whitespace (leave enough space for the DM to write in their own notes). Include photocopy-able handouts when needed.
-- tmaaas