The AI in this game is atrocious in many regards, but the worst offense has to go to combat AI. Both with the "plans" you use, and the computer opponents. Every single game Germany does something stupid. Stops attacking France because over half its troops are staring at Russians, won't support Italy in Africa or otherwise, leaves France unguarded for an easy American invasion in 1942, etc.
Japan either sort of steam rolls China and then stops, or again, does something stupid like committing a ton of divisions to the border of Russia and then they get wiped out of China. Or, they will randomly send divisions to India, to Europe, wherever, while their home islands and China are getting wiped out.
Italy stops defending Italy. I don't know how many times Rome is captured by some Canadian division invading.
And player fronts/plans, where to begin? Just as an example, the AI will throw divisions into a surrounded port(i.e. a trapped division that is going to die), after using strategic movement to get the reinforcements to a friendly port for naval transport. Big surprise, those divisions show up worthless and everyone dies. It also has this terrible idea to pull troops back from the front and then move them up with strategic movement right into battle. They just keep ping ponging.
What's the point of plans if you have to constantly be checking to make sure the AI isn't doing something really stupid? Even just mediocre performance would make them theoretically worthwhile.