A major issue for me that I have noticed is that the computers seem to focus on making the majority of their armies out of skirmishers. I have tried 2 groups so far, Rome and Parthia, and both of them have had very little difficulty in battles because all of the computers I run into are using armies with 50-75% of their troops being skirmishers.
With the Romans, I can easily out match most neighbors infantry with the more heavily armored infantry, and I can easily shatter skirmishers with support units (such as defeating 5 full units of skirmishers by sending 1 unit of war dogs at them, losing no more than 5 dogs).
With the Parthians, I was expecting both them and their neighbors to be heavily focused on horse archers like they were in the first Rome. But after trying them out, I discovered that the way that most units use their shields more effectively now make horse archers fairly worthless so I shifted to melee cavalry. This lead the computer's skirmisher focused armies to being worthless against much smaller forces, even with supporting spear men. I recently had a battle where the auto resolve bar was giving me about a 10% chance because I had about 1000 cavalry vs a 4400 man army and I ended up killing over 3K of them and lost 41.
With the Romans, I can easily out match most neighbors infantry with the more heavily armored infantry, and I can easily shatter skirmishers with support units (such as defeating 5 full units of skirmishers by sending 1 unit of war dogs at them, losing no more than 5 dogs).
With the Parthians, I was expecting both them and their neighbors to be heavily focused on horse archers like they were in the first Rome. But after trying them out, I discovered that the way that most units use their shields more effectively now make horse archers fairly worthless so I shifted to melee cavalry. This lead the computer's skirmisher focused armies to being worthless against much smaller forces, even with supporting spear men. I recently had a battle where the auto resolve bar was giving me about a 10% chance because I had about 1000 cavalry vs a 4400 man army and I ended up killing over 3K of them and lost 41.