BG1 had mediocre behaviouristic patterns for NPCs. However, i think that the best examples of party NPCs reside in Arcanum, BG2 and Torment. I'll explain.
In Arcanum, you could talk to your party NPCs. Not only that they reacted to what you did. In fact you could even make Virgil go evil (the climax being that Star Wars
esque confrontation with his mentor, Joaquin, in Caladon). Due to your actions he actually became evil. The voice and attitude even shifted. Beyond that, they didn't do much. There was something else which was also nifty, though - you could ask them what they knew about the current location.
In BG2, characters acted out of their own accord. Yes they were mostly timed events, but does this matter? NPCs in other games, BG2 included, acted based on scripts or timed events as well. I think that BG2 succeeded in creating a party dynamic on one side, but crippling it on other. On one hand, you were witness to some party members simulating a relationship of sorts (which, admit it, adds to that much touted immersion factor). They act like they are aware of things, and people in the party. Not only that, people could get emotionally attracted, but you also could decide how this romantic endeavour would play out. I get a kick out of trashing Aerie and tell her to leave my party when she got pregnant :twisted: But the system was crippled in the part where you could not interact by your own will. Everytime you wanted to ask Jan for a joke, well, tough luck - he, and all others, had "nothing to say to you". Bullocks to that. Strangely, fanmade mods for the game add this functionality for romance purposes. Good job, Bio, i can see where the idea to let NWN's community do your job for you came from.
In Torment, you could interact with your party member at will. You could engage with them in dialogue, trading impressions and learning skills with them (in fact you could even teach them out to improve some of their skills). But the problem is that they never spoke out of their own accord, only very rarely and as shortly as NPCs in BG1 (though PS:T's NPCs traded more funny comments they were still minimalistic). Though, how you treated your comrades actually influenced their morale, which had visible effects (like Dak'kon's blade strengthening).
I think that, what is missing from these games is the actual part where NPCs acted less like meat puppets and more like personalities. It doesn't make sense, in BG2, that i can't talk to my party members but can decide for them what i want them to specialize in, in terms of weapon proficiencies. It also doesn't make sense that none of the well crafted personalities in Torment won't speak their own mind except in scripted moments. Like mentioned above, why does a Paladin nonchalantly kills a street urchin, but then complains about the drop in reputation? Why did he even obeyed my order in the first place? This is a major problem in many RPGs. Unfortunately, this is more visible in BG2 because characters bitch about everything. I like it how Bioware states in the official FAQ that sometimes characters may disagree with my choices. Well, if they disagree why don't they actually *do* something, instead of just whinning? We have the example of Jan cursing me for making him attack the Sniverfrniblin (sp?) group in the Underdark, for the leader's helmet. But its rare, and its just a complain.
EDIT: Also another 2 thing in Torment. One, is that some characters wouldn't even interact with the rest of the party (like Ignus or Vhailor). Two, one thing you had the opportunity of doing on several occasions, was to ask their opinion on matters presented to you, like the Lim-Lim purchase. Again, unfortunately, this was little in amount.