These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Artificial Stupidity: Even on "Hard" difficulty, the AI doesn't present much of a challenge to experienced players, often struggling to construct any sizeable, competitive military force at all. The best custom AI scripts for the second game can single-handedly defeat a team of five default AIs, and it's not unheard of for dedicated human players to take on teams of seven AIs on "Hardest" difficulty (where the AI cheats).
Ally AIs generally do nothing but gather resources. This is especially irritating in any mission where you are tasked with defending an ally, given that defending yourself from the enemy is difficult enough as it is. Of course, then there are the times when your ally does actually train an army—a nonsensical, ineffective mishmash of units that they send off to their deaths one by one. This is particularly annoying in Online, where NPC armies have a random chance of training an Elite (more powerful) version of a unit instead of the normal unit. Seeing an Elite War Elephant be paraded across the map, being slowly killed by enemy units while not inflicting a single injury on those enemies, is a difficult sight to bear.