I don't have problem with sieges beeping somehow schematic -with preset entry points. it would be very hard to program and probably very buggy and easy to abuse otherwise. It is however much more expanded system from what Warband offered. My complain is that player can not really control troops much. Giving him control over what troops to attack/assign were (gate, laders, tower...) and when would be nice.
However I agree that defending AI is very bad right now. Shieldwall is completely ineffective formation for close fighting and having large group of men camping in front of the gate does nothing. They just get slaughtered. They should switch to charge as soon as gate breaks.
I also like your idea of AI being more tactical about tactical locations. They should be like defensive nodes that AI needs to hold or take in certain order and not just sending soldiers on ignore everything command to the location on the other side of the map. AI -both attacking and defending one should try to secure one "key" location before proceeding to attack/defend another. Every such location should have two positions, one for infantry and one for archers (different for attacker and defender obviously) and infantry should have certain radius in which they will charge any enemy, not just stand in the shieldwall waiting to be killed.