i Would like :
A multiplayer setup where you are able to play in lan or something like that with your friends and have multiable story finishes and startings , also that you and your friends would be able to finish the game in Cooparation style.
the train idea would be fun..
and maybe see alittle of the east coast and some old towns still standing in ruins like "Newyork or chicago(or how it is spelled)"
maybe be able to join sides , like be a raider or some anti mutant organizations or something like that.
and that you will be able to creat your own stuff but you`ll need to learn it. maybe modify your own gun , armour ect...
it would be fun if the game had lots of different options to.
that your character could be a fat guy and such some charactirstic weiws. new weapons and armours , and less bullets for your guns so the game is more depentet on survival without guns.
also that you need to feed character would be cool , the stress to find food and such.
some new monsters and leagues , Mafia organizations , some Anti Brotherhood of steel groups or new BoS typish groups..
Jetpacks could be cool :p a few trap options , like trap doors with explosives , digg down mines and such .
more dialoug options.
half-mutants .
Ghoul towns
Mutant towns ^^
or some other group of humanoids.
Cannibals
groups that try to raid sometowns and such.