Morrowind 100%. I've got both. I paid $90 (CND) for NWN, and only $40 (CND) for morrowind. I feel I paid too little for Morrowind and WAY too much for NWN.
As for the whole open ended/restriction based thing, it depends on what kinda gamer you are. I, personally, always find myself getting angry at games that dont let me "just explore", and there's heaps to do.
I guess it boils down to do you want a liniar game thats spoon feeding you what to do, or a game thats so open ended you might feel overwhelmed.