First time player recently finished BG1, now several hours into BG2.

I recorded some video to show my problem:

http://www.youtube.com/watch?v=Of-7K0v-tVo

At the start of the battle I have all 6 party members selected and I click on an enemy to attack.

In BG1, this would often be the extent of input required for a low-level battle like this, and my party would mop up the rest of the pack by themselves without any further input from me. Now all of a sudden in BG2, as you can see half my party is sitting idle after the first creature dies, as if their AI is not active (party AI is on).

This would never happen in BG1, the party did not need inputs just to be told to attack the enemy *that was attacking their fellow party member right beside them*

I know there are some kind of scripts you can set up to change behaviours however I did not need to touch that in BG1 so does anyone know what's up and is this normal for BG2 ?

I'm not sure if there are script commands to change this (you'll have to check them out), as I always take control myself, but there are several different creature types in that group. The AI, in BG2 at least, seems to only automatically go to the next target if it's the same creature type (such as if your first target is a Phase Spider, then the AI will automatically target the next Phase Spider, but will not auto target the Sword Spider. Different creature.)

Coelocanth is correct. This is no different than BG1. The AI will only continuing attacking creatures of exactly the same type as those instructed to. For instance, if you instruct your party to attack a group of Goblins in Irenicus's dungeon, they will do so, and then proceed to ignore the Goblin archers behind. This is just how the AI works.

I'm guessing that maybe there's more creature diversity in BG2, so the issue becomes more obvious?

Quite possibly. People should also be aware that the default AI scripts are pathetic at best. For instance, the default melee script will only kick in if the fighter actually gets attacked. The default ranged script will kick in when an enemy is in range, BUT if the party gets jumped the ranged script becomes a liability, because the archer will run away (to get out of melee distance), but the script is broken in that the archer runs FAR too far away, and often the fight is over before he/she returns fire. The eSeries scripts are far superior for those who like to have AI enabled.

Edit: by way of illustrating the level of pathetic in the default scripts, here is the default AI script broken down (I am assuming it is assigned to melee fighters, since there is a default ranged script). Also note that all script lines are interpreted sequentially: So, what does this mean? It means that

a) [first IF] if an enemy is within weapons range (1 unit for long swords, 2 units for two handed swords), AND the unit is not doing anything else, that unit will attack the nearest enemy for ONE ROUND.

b) [second IF] if the unit is attacked, AND it is doing nothing else, it will attack whichever creature attacked it for ONE ROUND.

And that is it. That is the entire default AI script.

I've been controlling my characters using the autopause the whole game, so haven't really used the AI scripts. I would like to know, though, what happens when a character (specifically, Minsc) becomes beserk. Does he use the ai script he currently has active? The default AI script? Neither seem likely, as in my last encounter (note that I hadn't changed his script from default), he was quite happy to charge at another area with fighting going on when he'd dealt with his own. Also, I doubt that the default script would cause him to attack his allies if there are no enemies available :P

Do you happen to know what the beserk scripting is, and if there's anything I can do to influence it? Obviously I'm not expecting to be able to affect it too much, that's kind of the point, but if nothing else I might at least be able to position him better and activate the beserk at a better time.

Berserk is handled by the engine: you can't effect it. What it does is gives Minsc 16 immunities, a strength bonus, a dexterity bonus, removes fear/panic and resets morale -- he is then immune to any such effect -- and makes him unpredictable. In this state, with a ring of freedom or Spider's Bane (for stun), he is a lone Mind Flayer executioner! Under fair circumstances he is still controllable by you, but unpredictably he will literally go berserk and you lose all control. Minsc's Berserk is best used by sending him into a situation alone, or trigger it and then get your party the heck out of there, because he will turn on the nearest party member if no enemies are nearer. An invisibility potion for healers is the order of the day, in case he gets into serious trouble.

In my brief experiences, he seemed to lose as soon as we saw an enemy (or near enough), and remained so until shortly after we'd killed the last enemy. I ended up running Yoshimo around the party, followed by Minsc. The downside of giving him a ring of freedom, I assume, is that you then can't cast a hold spell on him if he goes out of control?

You can't hold Minsc when he is berserked -- in that state he is immune to domination, charm, dire charm, fear, panic, Illithid mind spells, energy drain, level drain, confusion, sleep, maze, hold person, hold creature, hopelessness, chaos, feeblemind. Don't waste your spells, just keep away from him, or go invisible.

The Fighter1 script does this. If the character sees an enemy he/she attacks. The danger in this is that your mage and thief will run into dangerous situations without any thought. The most comprehensive scripts in terms of versatility -- as far as I know -- are the eSeries scripts. Give them a try, but be sure to read the documentation carefully, because they use complicated 'shouts'.