Hi.
I'm Huge fan of Fallout series.
First:
One of the things that I've always wanted is.....: Vehicles!
C'mon Guys. On Skyrim, Oblivion there are horses and they hmm work?
Only Fallout which has vehicles is Tactics, and of course you've couldn't drive on whole map (except one or two maps of 20).
I don't think it's such a big deal for not making it. Especially when the newest interface gives players such huge amount of creating almost everything what you want.
Can You imagine creating Your own special vehicle and drive it whrough wasteland instead of infinite running?
Second:
Make more places with humans, more cities, towns, or little villages / towers / small communities with people whom You can talk / barter / quests etc.
It was a huge waste of potential imho in previous game. Except couple of cities, the rest was always Riders or Ghouls, which makes sometimes the whole running through Wasteland simply bornig.... (imho of course).
Best regards
p.s. hardcoe mode - don't forget it!