My current greenskins playthrough I've been annoyed at the dwarfen predilection to making armies made up of around 6 quarrelers, 2 grudgethrowers and everything else longbeards. I know they're better units than the warriors but... thematically I feel they shouldn't completely replace basic infantry with elites. I could make an army of big 'uns, black orcs and so on to counter it but that's gives me the same thematically wrong problem now on my end.
I also think the A.I. should be a bit more aggressive, I suppose. I get frustrated at the A.I. avoiding combat. Send army with backup against enemy army, enemy army retreats to a point where you can't attack with both armies again means you have to wait till next turn at which point they'll have force marched out of your reach or used the underway.
It's the idea that the A.I. is playing smart by avoiding my armies and attacking where I am weakest which is nice but having the A.I. attack only when it is sure it will win I feel leaves me with only one sided fights. I think it was mentioned in some article that a game A.I. should idealy be strategically dumb.
Example: I hold a bridge with an army. The A.I. wants to attack my city behind my army. A smart A.I. will go around the bridge, avoiding the battle and making my defence useless. A dumb A.I. will attack my army on the bridge even though it's at a disadvantage. I would find the second outcome more enjoyable because I used the terrain to my advantage and got a nice stomp-the-A.I. battle out of it. The only response to the first scenario is for my army to be in the city, which would probably mean the A.I. wouldn't attack there and they'd go off and attack another of my cities where I don't have an army.