This is an odd question in that it can be taken a multitude of ways. I think I’m going to go with the game campaign that most surprised me…
In 2010, my game group blew apart due to my divorce. About half of it remained intact, and we had to start a new set of campaigns to account for this. The one that most surprised me would have been out Hollow Earth Expedition game, which was set in 1936 Shanghai, a few months before the Japanese pulled the trigger on their invasion. The characters were a tough, unprincipled archeologist who had a reputation for being more tomb raider than scientist, his action-first, thinking later sidekick, a half-Chinese gangster, and an 12 year old female Chinese street urchin.
Rather than stumbling along, the adventures just flowed — from the introduction of the McGuffin, evidence of and possible means to find a mellified man, to trouble with the Japanese and other gangsters, to Nationalist politics where they had to rescue the president of China from his generals (and in the doing uncover the Terracotta Army a few decades too early.) They travel into deepest China to a monastery, battling an old sect of warrior-monks led by “a woman who cannot be killed”, found the mellified men, the girl accidentally ate a piece and was possessed by the spirit of an ancient warrior who wants to rule all China, to a final showdown in the underground tomb of the first Sovereign Emperor and his terracotta army.
The birth of my daughter and the moving away of several players brought the campaign to a close, but it was a good stopping point. We had another couple of adventures where the first two characters were battling Nazis to find a “lost Illuminati treasure” that first looked to be in Virginia, then turned out to be buried under Ben Franklin’s house in London.
Overall, the speed and ease of the plotting, the level of fun had, and the creativity of the group seemed revitalized by the changes it had gone through, and makes it one of my favorite campaigns I’ve ever run.