The only two I've liked was the Y'sthola duty in SB (I don't even remember why I liked it, maybe it was the first "role play" duty that I noticed being different) and the Thancred solo duty in EW. The Thancred duty majorly reminded me of base infiltration/stealth, limited unit missions in old RTSs like C&C and Red Alert. I enjoyed that one a lot, I just wish it was harder/easier to fail.