Like Thane, I liked the freezing gimmick of Conquest 21. I brought a full team, and getting them all through while killing only what was necessary and making perfect use of DVs was great fun. I also enjoyed Conquest 15's replica gimmick. The rest of the maps I liked was more due to good design than gimmicks.
Having played through all of Birthright and Conquest, as well as half of Revelations, I was only really bothered by the pot chapter in Conquest (forgot the number). They only served as annoying time-wasters to me in a map where you already have to rush, with an unappreciated element of unpredictability added on because you can't tell what the effect actually is, only if it's good or bad. Even the fox illusions and snow shoveling chapters were leagues better for me because I could just play them safe.