At Gen Con this year we're hosting a seminar on how to write adventure modules. As preparation for the seminar, here is a list of things I look for when I get a submission for the Dungeon Crawl Classics line. A good adventure doesn’t need to have all of these items. But most good adventures do have many of them.
• A sense of the fantastic. Convey this through encounters, descriptions, and most importantly, magic. The fantastic is what makes D&D so much fun, and that has to come across in the adventure.
• Memorable encounters. Avoid repetition. Consider all aspects of an encounter: timing, environment, opponents, hazards, battle conditions, and so on. Think about templates, feats, equipment, magic items, and spells as ways to make opponents interesting. Try to come with ideas for rooms that players will still be talking about 20 years from now.
• Hard work on thinking out great encounters. Dungeons with stirges, darkmantles, chokers, rust monsters, orcs, and other no-brainer monsters strike me as lazy. The job of a published author is to produce material that the typical DM at home could not produce. Don’t submit derivative dungeons.
• New twists on old classics. Don’t throw in a rust monster. Instead, make it a rust spider that climbs walls. Players will never suspect that the reddish-brown spider attacking them actually has the same stats as a rust monster. Surprise the players!
• “Easter eggs” – at least one well-hidden room with a cool treasure of some kind, accessible only to very diligent or very lucky PCs.
• Intelligent treasure. Why give gold when you can give art objects? The treasure should match the villains and location. Sometimes the best treasure is information, because information leads to more adventures. The classic example is a treasure map; other options include blackmail lists, diaries and journals, or spell books with new spells requiring rare adventure-worthy components.
• A good villain. Not every dungeon crawl needs one, but the best ones often have them. The adventure has to establish a strong emotional framework for the villain, too; it’s not enough for him to just be “another evil necromancer.”
• Sequel potential. The DM should be able to continue the plot threads begun in this adventure to create future adventures for his campaign.
• Distinctive levels. Each level of the dungeon should feel distinct from the ones before and after it. They shouldn’t blend together.
• A strong narrative feel. Usually this is a buildup with a climax in a big encounter at the end, but that formula can be varied. Regardless, focus on an encounter list that forms a storyline that reads like a great adventure novel.
• Secret doors. Every dungeon needs at least one secret door, preferably hidden in a place the PCs won’t think to look. Secret doors at the bottom of pit traps, secret trap doors mounted in the ceiling above normal doors... think of ways to fool the players.
• Thought requirements. There should be at least one puzzle. That doesn’t necessarily mean a riddle. It could be a room that’s hard to figure out, or a strange new monster that can only be defeated in a special way that’s alluded to elsewhere in the dungeon.
• Good pacing. Long, tiresome combats should be followed by quick rooms. Thought-provoking puzzles should be followed by bloodbaths. Slow, trap-filled hallways should be followed by a rousing fight.
• Group involvement. Meter the action so there’s an even mix of involvement by all character classes.
• A twist, preferably at the end. Establish PC expectations through read-aloud text, then use those expectations against them to create plot twists.
• Subplots. Subplots vary widely, but the best ones have a few things in common. First, they involve several PCs in an ongoing drama of some kind. Second, they create mystery or intrigue. Third, they lead to potential future adventures.
• New monsters. A new monster that throws off the characters is good (as opposed to simply duplicating the role of an existing monster, which is a waste of space).
• A “cut to the chase” feeling – start with a bang and get to the action fast. Don’t waste time on empty rooms unless they really add something.
• Intelligent ecology. Most monsters need to eat, sleep, and drink. Dungeons should allow for this fact.
• Atmosphere. The dungeon should have a strong, cohesive vibe of some kind, whether dangerous, or evil, or disturbing, or reptilian, or whatever.