Companion dialogue.
Companions seems to run out of stuff to say after a while and when that is lost then they're no better than a merc for hire.
Make it so that companions have a lot of dialogue and that some of it unlocks itself at certain areas, after talking to certain people, after completing certain sidequests, or after you advance more and more in the main quest.
Make companions have influence as well.
If a companion has high lock pick skill then let us utilize it.
If they have high speech let them speech check the dialogue for us.
If they have high repair/traps skill then have them say "Hold up, traps ahead" and go disarm it for us.
Also make them have their own morals.
Like, Boone will just shoot legionnaires, and whatever, that's fine.
But I want companions to go "Wait.. You're going to do WHAT!? Listen, you do this, and we're finished, in fact, I'll kill you if you try to help that person" if you try to help oh let's say an "evil" person do a "evil quest" while you have a "good" companion with you.
Just make them feel more real, like they have their own morals that they won't break.
Even make them turn on you if you try to go against them. (Depending on what the situation is about)
Maybe a scientific companion which values advancement in tech above all else.
If you try to kill a bunch of people who uses slaves for chem experiments then he will turn on you.
He doesn't like that they have to use slaves as test subjects, but in the name of science you have to leave your morals at the door.
The slaves might become heavily addicted to the chems, maybe die, maybe even mutate depending on what kind of chems there is.
But what if they manage to create a new chem which could help a lot of people?
Would it be worth it?
This guy thinks so, and no matter what you say or what you want to do he will not listen to you.
Make it so that we can have 2 humanoid followers which also interact with each other. (Again, they will have new stuff to talk about when you trigger area/quest/dialogue events)
All this and a little more. Make the characters feel even more alive. Make them more than just someone you bring to a fight. Make them even interact with the world like you have team up with a guy that is a good friend with Mick and Ralph so therefore you get a discount there, but he's also in debt with the Omertas and sometime before he also worked with Benny and they didn't get along so if you have this companion with you, there could be different ways situations turn out, and Mick and Ralph might give you a discount or access to even more special items.
And you should be able to have two followers, and they'd all have different personal chemistry so some companions will dislike eachother, not work well as a team and maybe even leave, or some do the opposite, and when you wander the wasteland they could talk about whatever, either they agree or disagree or agree to disagree. Could be NCR-CL politics, or it could be about battle cattle.