For me a toddler with an Arnold Schwarzenegger face and voice who is also a scientist.

Blood thirsty hoards of rabbits.

That guitar guy from NV.

A crazy guy who thinks he's dragonborn.

A cliff racer.

You fool! You'll kill us all!

I wouldn't mind some Fallouty Cliffracers. Just so I could reenact the Cliffracers Massacres of '04...or whenever that was

Grenade launchers

Robot building

Personally, an Enclave Remnant like the one in Fallout New Vegas. Not an organized force, but rather a small number of ex-Enclave members who fled the Capital Wasteland. I want to be able to persuade them to join my settlement and bring their knowledge and expertise to the table to help the people of America, rather than to eradicate them. Of course, I would also love the option to completely wipe the remnant off the face of the earth, or to just leave them alone. Just a couple nice side quests with 4-5 Enclave members as possible citizens as a reward.

At least one member of the Midwestern BoS. So we can find out what is canon from FTactics.

A Institute Synth facility that has malfunctioned and is producing replicant versions of a certain trader in Megaton.

Moira Browns.

Moira Browns everywhere.

Companions that actively participate in dialogue and comment on your choices.

Well....

1) Some sort of encounter with the Puppet Man from Vault 77 would be great. In my mind I've connected the Puppet man with the Mysterious Stranger that shows up randomly in combat from time to time, even though he always uses firearms...

2) Some sort of town put together and ran by a bunch of repurposed Mister Handy and Mister Gusty. Maybe controlled by a central computer...I know we've seen it before in the fallout universe, but it's something that never gets old. At least to me. They could cause problems by raiding other towns for salvage, and maybe by raiding YOUR town for salvage.

3) I would love to see some Garys too. GAAAARRRRRRYYY!

Thought about this today while playing New Vegas...

I'd love it if Sunset Sarsaparilla could be found. Not a lot, just a bit.

Seeing your spouse alive, albeit as a ghoul. Also being able to romance your ghoul wife.

One of the things I love about Bioware is the banter/arguments between companions.

I'd love to be able to have more than one human companion at a time especially if they actually talked to each other.

As is, I'm hoping the human companions in Fallout 4 are a little more active/verbal than last time.

Willow was one of my all time favorite mods in Fallout NV.

Abbbb sewww - looot leeeee !!

Mr. House before his exodus to Vegas.

more party banter from companions. As much as I loved Cass in NV, only so much "shhhhh, we're hunting [censored] heads" can be had before it gets stale.

I second the notion to be able to make robots. heck I wouldn't mind making them to protect my settlement from raiders.

I'd like to be able to form my own or join a raider faction and go on raids.

Vehicle repair and driveable vehicles. I mean we can build and arm settlements right?

I would love to see return of star trek easter egg

Clover.

And don't charge into groups of dangerous enemies, I keep on this side of this corner for an reason.

They should at least notice land mines I put down, like the one behind the corner where veronica make her stand if not charging.

I was gonna suggest mini-nuke mines.... but this is a MUCH better idea.

Oh, and an actual Vault 13 jumpsuit.