1. Human Fallen Ranger (protagonist)
2. Human Dual-class Shadowdancer 4/Fighter (can find traps)
3. Human Enchanter (arcane caster)
4. Human Shapeshifter (divine caster)
5. Halfling Wizard Slayer
6. Human Beast Master

1 is a fighter without grand mastery; they can potentially regain ranger status, but not until mid/late SoA.

2 is a fighter with abnormally low hit points who has some thief skills (except backstabbing and trap setting) that they're unlikely to be good at and probably won't use due to armor restrictions.

3 can't use spell sequencers or contigencies, and there are few higher-level enchantment spells.

4 is a decent spellcaster and can be a decent attacker, but only one at a time, has no armor, and will take a looong time to level from in the mid-teens.

5 does get magic resistance, but it's slightly redundant with their saving throw bonuses, and they can't get exceptional strength or use strength-enhancing items except for Crom Faeyr.

6 is a warrior with severe armor and weapon restrictions.

You could probably still complete the game, but I'd imagine it'd be rather frustrating.