Now, about the AI. I haven't looked at the maps yet, but in the Campaigns...Magnus just sat in his castle, occasionally venturing out to defend a lumber mill – and that's it!
And in the previous mission, Solmyr wandered around the underground realm of the lovesick necromancer for months, and the necromancer didn't even lift a finger to stop the djinn's rampage!
Damn it, I've played through 3 Campaigns – only in the Barbarian one did I have to defend my city a couple of times; in all other cases, the AI gave the initiative to the player from the very beginning.
But in Multiplayer, the game is really great.
Well, the computer in Heroes 4 is incredibly stupid, although sometimes it manages to assemble a decent army. It behaves most stupidly when defending its castle, especially when it has archers, even if they are very weak. It doesn't even leave the castle, even if you accidentally eliminate these archers, no matter what army is inside – it's a real gift for Nature and Order.
In my opinion, I don't like offline play because of all the "absolutely" illogical actions of the computer. Building your game around observing and finding the quirks of the computer is...well, it's just not the same. It's more interesting to win by using your own mind, not because of the inexplicable mistakes of the opponent.

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!