How about having a more fluid hand-to-hand combat system so it feels like im fighting rather than swinging and hoping i hit something.
Make it so every 5 minutes my xbox doesn't crash or something doesn't lag out every 5 minutes.
Bring together all previous factions from the past and then add some new ones as well.
Have the main character be an american in china.
The story could also be set in a remote place like Hawaii or the phillipenes.
Add vehicless to make travel faster but not pointless like fast travel.
Have a different crosshair that actually will be where the gun is shooting(I like the classic 4 lines and a dot in the middle).
Make decisions in fallout 3 and NV affect the story in 4(ex. Mass Effect on a larger scale).
Make it so I dont have to take 4 or 5 trips to bring all of my unwanted stuff to the store(like a mailman system).
Fix the glitch where my guy stopps shooting and just stood there while being attacked in VATS(glitch ocurred in 3 and NV).
Have more customizable companions. Not one companion was a friend of the Legion som I had to fly solo(ex. a brother, girlfriend, sentry-bot, pet deathclaw that are with you from the start that share your views).
Bring multiple(like 4 or 5) companions so yo can have your own little death squad so you dont have to storm a deathclaw cave with 3 people.
Customizable houses(wallpaper, bring back the robotic butler, more/different furniture, expansions).
Make it so there is no anoying, all-knowing, computerized faction leader.
Fix the damage scale(the missle launcher should not do less damage than the AM rifle).
Have duel-wielding pistols/smg's.
Customizable armor(ex. color and upgradable statistics, looks, and special capabilities).
Better iron sights so you can actually see what you are shooting at.
More random faction battles(they look cool and allow you to side with the one of your choosing).
More interactive invironment(shoot through/destroy walls/buildings, deadly land conditions).
Be able to give more precise orders to your companions.
Like previous member said, you should not be able to pull a minigun, power armor, and 345 5mm rounds out of a chunk of a mutilated foot. The guns, ammo, and items should be scattered about and the armor should be beyond salvageable if a body explodes.
Be able to become a part of more major factions and not just work for them.
Develope more advanced forms of mutants and ghouls(bring back the behemouth!!!!!).
More guns with special affects rather than every one shooting bullets, missles, laser or plasma.
Make it so there is less loading(not every time I go through a door). Also, give me an option during quick travel if i want to spawn inside or outside a building so that, first of all, i dont have load twice, once during quick travel and another when im entering the place and second, I could spawn outsid so that I dont spawn in a room crowded with enemies.
Thanks for considering a few of my ideas.