I can't wait for this inevitable game! I plan to pre-order it without even knowing what or if the pre-order bonus will be. I can't wait, with Skyrim (which I did enjoy) I can say that the Fallout series has safely passed the Elder Scroll series as my favorite Bethesda series.
As for what I'd like to see, well...
More wacky, dark humor and the ability to change your characters back story a little bit, like choosing to be a Vault Dweller, a Tribal or a Raider and then getting different events and outcomes based on that decision. It would also give the intro quests a little more variety since they always get old the fifth time I play a game through.