Personally I'm glad they got rid of Dwarven mines, since it often make other resources unharvestable once I discovered then on a mined tile (If if were still possible to replace improvements and stop enemies from pillaging then I would be fine with re-introducing them
Citadels still sound more like forts that just sentry towers to me. Also, if forts now use the city code as has been suggested, their special ability might be a little easier to implement (just a wild guess)
I would like it if multiple civs had special forts. For example, now that forts can act as canals the Pirates cove would be better if made into a fort that could blockade nearby rival trade networks without the need for actual pirate ships in the vicinity (or perhaps it should increase the ships blockade range an/or provide extra trade networks). Perhaps the Chancel of the Guardians would also make a nice fort, one that automatically sanctifies all nearby terrain and perhaps (either randomly or temporarily) grants the defensive promotion to the units garrisoned there. Since I believe that BtS forts can be built in neutral territory, they could build a network of these surrounding the Infernal Empire to keep hell contained(personally I still think that hell spread needs to be fixed so that good players actually need to work to keep hell out of their lands, at least at a high AC). Magical boni for Sorcery spells cast in Amurite and Summoning ones in Sheaim unique forts would also be a nice addition (like increased strength and/or range, possibly tied to the amount of the appropriate mana possessed. Affinity adding promotions for the summons created there might be nice). I could probably think of a few more if I really wanted too, but these 5 seem best.