Even if there hasn't been a huge rewrite of the AI codewise between Dom2 and 3, it has been improved significantly (the AI build castles, doesn't take scales as destructive, builds better troops also), and the Dom3 setting is much more AI-friendly : more gold, more resources mean more conventional armies, that play a bigger role up to the mid-game. PD is also usually bigger and allows for a defensive boost in the early stages also.
In my few Dom3 test games I've had difficulties to just survive the 20 first turns vs "difficult" AIs when playing on a crowded map (Silent seas with 5-7 nations).
Very good so far
