I just really miss being able to cast spells/summon fire elementals to defend cities.
Right now, if a city gets hit by a wandering monster early, I just lose the city. Late game, it's easy to have a huge stack of units that can just stomp through any city guards.
It feels very un-fun trying to defend cities. Sins has the same problem... either I split my army up among the entry points to the empire and still get rofl-stomped by a single big army, or I do the single big army and rofl-stomp them. Just like Sins, it takes an incredibly long time to move your armies around, so responding to an incoming assault just isn't possible. That mechanic is the core of why I think Sins is boring and why I'm not enjoying a conquest victory in Elemental.
Civ solved the problem with free-movement railroads. Galciv solved it by making later engines more powerful.
If I can't move my strong heroes around quickly enough, then I need to be able to use magic to defend cities being attacked.