Indeed, I didn't comment on multi or dual classing because that just changes everything. I haven't played any of the 3rd/4th/5th edition games, so I am unfamiliar with those rule sets. But I wouldn't be surprised if multi and dual classing were heavily nerfed. They really are just too much...unless your character is actually a demigod.
But again, the fact that they allow you so much freedom in creating your character is incredible. You can even triple class! I sincerely miss this kind of freedom combined with the incredible depth of the AD&D 2nd ed rules.
I'm looking forward to Pillars of Eternity, but I'm quite sure that mechanically it won't be nearly as fun as BG2. Those developers just know better than to implement such insane mechanics again. Which is why it won't be nearly as entertaining.