B10 - Night's Dark Terror. 64 pages that can pace an entire campaign. The maps are fantastic, and the lead in to the adventure is great. The detail is better than any other module, but can easily be ignored if you don't want to worry about the primary features of background NPCs, treasure, etc. The adventure allows the PCs to work as a team in defensible positions, assaulting dungeons, thinning out an enemy hoard, uncovering city mysteries, tracking & espionage, exploration of uncharted lands, diplomacy with other races and fighting new nasty critters. There are enough mini adventures and side trips to keep a campaign going for a year with plenty of places for interludes to sell treasure and buy new equipment. Plus there are BBEGs that just make the players hate them from the start once they are uncovered. There is so much goodness in that one module, it's tough to mention it all. Oh, and it came with counters for a major fight, which was crucial for the OD&D days of pre-plastic minis.