One of my major loves about the Baldurs Gate and Icewind Dale games was having different AI scripts available to customize how each character was controlled by the computer, but also with how those scripts would suspend for a period or adapt if the player told that character to do something. Many of the newer games, such as Neverwinter Nights and Neverwinter Nights 2, did not seem have that same level of AI.
I won't lie. I'm not super huge on having to micromanage or give orders to my party members every round in combat, but I do like being able to tell my party members to do something from time to time, and have them do it before going back to to their AI. I want to be able to have my party prioritize a target until that target is dead. I found a lot of the time in Neverwinter Nights 2 that the AI would be trying to change targets every 2 or 3 rounds, despite me actually telling them to attack someone.
I guess my point here is: Please make sure to do party AI right. Have AI in the game to take over when the player isn't directly telling the party what to do, but allow player commands to trump out AI commands. Whether AI is done using a script system such as what was used in Baldurs Gate in the past, with a user defined priority system where they can use dropdown boxes to set up something like "When <ally HP> is <below> <50%>, use <skill>", or some entirely new system to determine how the AI should react in a given situation, frustrating Party AI can definitely ruin a game for someone like me.
Please take the time to do party AI correctly.