A big draw for me in these games (especially in the long run) has been finding, trying and playing interesting class combinations for the main character.
I would like to suggest an increase in the available multiclass (and therefore dualclass) options: druid/mage, druid/thief, even druid/sorcerer or barbarian/x should all be feasible. I would also like to see the wild mage made available for mage combinations.
It would also be neat to see more of specialized multiclasses (like the gnome illusionist/x) to give a greater incentive to pick different races. For example berserker/x for dwarves, or barbarian combinations for the half-orcs.
Either suggestion would also broaden the field for more and more interesting new npcs.