Skills and Perks
Big guns and small guns return as different skills
Old perks make a return.
New perks ( obviously)
More perks have a catch, so as not to be overpowered.
limit intense training to three uses.
Weapons
Have new weapons manufactured by wasteland factories, like the Gun Runners.
These weapons should be designed like some of the weapons in the metro series, minimalist,survivalist and made with scarce materials in mind.
The new guns are cheaper, but don't deal as much damage as weapons made with pre-war schematics, very durable though and equips/reloads faster, as well as being lighter.
Way more energy weapon types.
Make them rare to find/expensive, but deals higher damage than guns.
Equipment/Gear/Loot
Stimpacks are less common, instead, like in J.E Sawyer's mod, have Stimpack (EXPIRED) and homemade stims.
Energy Cells/MFCs are a lot more rare than conventional ammunition
Food is rarer , only surviving pre war food is dehydrated or in cans.
Home cooked food like Brahmin Steaks and Gecko Steaks are more rare
Cooked Brahmin Slices and Cooked Gecko slices are a more common, but are only half as/quarter as nutritious as a steak.
Drugs are more dangerous, drugs like Psycho give you more damage but can lower damage resistance and on hardcore increase sleep and thirst.
Drugs also have the possibility of having a dirty needle, giving you infecion negatives, until you see a doctor and get cure of course.
Engine/Gameplay/UI
Developed on Unreal 4
Developed primarily for PC.
Dynamic Crosshair for different weapons like in Project Nevada
VATS given some major changes, since most players aim exclusively for the head and never any other limb.
Hardcore gets a major revamp with certain features and rebalances from Project Nevada implemented, like increased radiation gain, food no longer heals and Fast Travel from the Pip-boy is disabled, Caravans and the like allow for fast travel at a price, or you can hitchhike with a survivalist group, if you find one, and you find one going your way.
HUD text is scaled down and has an option to fade when not needed.
Wrist mounted PIP-BOY 2000, with some aesthetic changes for it to make sense.
Other
More unopened Vaults, with the inhabitants inside, and if it can be avoided, can we be rid of that dreadfully stupid experiment idea, I never really liked it in the first place.
Perhaps a non-Vault-Tec Fallout Shelter/complex that is successful? or a community that emerged from one?
Super Mutants and Ghouls need a redesign after Fallout 3.
Also Developed by Obsidian.