Sorry if it is a bit long.
I read some threads talking about party conformations, with multiclass characters, pure classes, doubtful about tanks, rangers, etc.
One possible strategy which I did not read about yet is delivering damage with tanks using magic mainly defensively by increasing character abilities and bonuses, healing, dispelling and if required summoning (more as decoys than anything else). In this case a Wizard or Sorcerer will not be required and you can replace it by a useful Bard. There is area effect damage that can be delivered with potions by thieves and also there is plenty of magic bound to weapons as well specially in the Hof mode.
About the issue of single class characters, IWD2 makes a multiclass character party to have clear advantages comparing it to a pure class one. I am talking here about how to get a more efficient party; a different story will be if you want to have extra challenge. When I talk about multiclasses I am saying to combine no more than two classes per character, as useful three or more classes combinations most probably will result in XP penalties even in humans. Two classes are obviously a huge benefit when combining fighter classes (Fighters, Paladins, Barbarians). There are no penalties to the BAB or HP by doing so and you will only loose some feats points. Nevertheless if the character is properly planned all the necessary feats will be obtained, but with the added benefits of the double class. I left Rangers out as they are clearly weak, being their only exclusive benefit the racial enemy, and if you want to make it an advantage you will have to allocate almost all your levels in this class and I do not think this feature is worth the investment. I saw lots of people mixing the ranger with a thief for the free two weapon fighting mode, but I have to say this mode is not good as it was in BG2. In IWD2 I notice is not as efficient and finally I found that by double wielding you just get 1 extra attack with penalties for both the main and off hand weapon. That is if you are a level 11 fighter you will have a total of 3 attacks per round with the main hand and 1 attack from the off hand, yes only one not an other 3 as it is suppose to be (check it in the characters info while wielding two weapons) giving a total of 4 attacks but both hands with –2 penalties, considering obviously you have all the appropriate feats and you are using light weapons. I would say this mode of fighting is only good for a thief when back stubbing (one extra attack in one round might be the difference between poison or not a backstabbed mage) using light swords and hopefully the offhand sword will magically give AC bonuses. Anyway if you really want to double wield they will be much better off with a fighter-thief mixture, which will allow you to have also weapon specialisation and more feat points to allocate.
Now here there is a successful Tank based party example with no wizards:
1. TANK1- LEADER:
Human or Aasimar, Pal 2/Fighter X (two levels of Pal for immunity to fear + aura of courage + charisma savings) specialised in bastard swords and Party leader.
Abilities: if human S18, D12, C16, I3, W9, Ch18
if Aasimar S18, D12, C18, I3, W9, Ch20
2. TANK2:
Half orc, Fight 4/ Barb X (fighter 4 for the weapon specialisation + extra abilities) specialised in great swords.
Abilities: S20, D18, C16, I1, W18, Ch1
3. TANK3:
Shield Dwarf, Fight 4/ Barb X (fighter 4 for the weapon specialisation + extra abilities) specialised in axes (double or single handed- double make more damage).
Abilities: S18, D18, C18, I3, W18, Ch1
Note: Tanks would invest in the feat: power attack-cleave (at least one slot)-dirty fighting-improve critical-dodge-weapon specialisation (focus in one) and finally saving related once according to weakness (as a fighters you definitely do not need great fortitude). Dash if extra points are available.
4. SPELL CASTER1- HEALER1:
Human or half elf, Bard X (the choice of races are only for if you want to multiclass with 1 or 2 levels of Barbarian for the extra HP an fortitude saves, or something else but you want fist at least to achieve as fast as possible Bard level 11 for the +2AC-healing song. Once this song is achieved the tank party is unstoppable).
Abilities: S6, D16, C12, I14, W10, Ch18
(Some ability points on intelligence for extra skills: identifying-alchemist-spell caster character of the group).
You can use this character also to do the talking and receive rewards.
5. SNIPER1- THIEF
Halfling, at least fighter4/ rogue X (actually it should be a balance between the two classes, as I do not think so many rogue levels are required so depending on the game stage more fighter levels can be added-for extra BAB and feat points) Specialised in bow and small swords with weapon finesse.
Abilities: S11, D20, C16, I16, W10, Ch3
(High intelligence for thieving skills. High dexterity for AC and Sniper role).
6. SPELL CASTER2- HEALER2-RESURRECTOR-SNIPER2-SEMITANK:
Human or half elf, Fighter 4/ ClericX, specialised in crossbows (spoiler in dark blue at the end of the thread) and hammers or long swords (could be a cleric of tempus and have axes to save feat points but as the dwarf uses the double axe I would prefer to have alternative weapons, you know for variation purposes)
Abilities: S16, D18, C18, I3, W18, Ch3
I hope this is useful, for game experimenters
There is an excellent crossbow in chapter 3 (I think) wich gives you 4 attacks per round!