IMO, I felt that two-handed weapons were underpowered in Oblivion; I could use one-handed weapons and still be just as deadly as any two-handed weapon user and I could carry a shield. Now with the addition of dual-wielding and shield bashing, I think that two-handed weapons should be made more powerful so that it would remain an attractive choice. I want two play as a two-handed weapon Nord guy in Skyrim, but I'm afraid it might be underpowered.
Also, I read somewhere that different items have different blocking capabilities, so hopefully two-handed weapons can absorb/deflect more damage than a one-handed weapon.