Normal AI means it gets the same number of points for castle/scales/pretender as you do. Weak gets less, Hard gets more than you. The AI's "intelligence" is mostly by being random. Such as, it wanders its armies so that you cant figure out where to meet it in battle.
The game itself has no option for random opponents but visit the Random Support Site at
www.dom2minions.com
There are .map files you can download there which will use the Aran map that you got with the game and start a game with random opponents (they are also randomly allied with each other). Since its only possible to do it with a .map file, those files are re-rolled every day with new opponents.