4. Better Story
I think everyone can agree that the New Vegas storyline was bad. It consisted of one faction or another trying to take over Hoover Dam, with the only difference being that one is portrayed as good and another as evil. Fallout 4 needs more likeable characters, people that you can connect with. I felt no attachment to any character in New Vegas, because they just weren't likeable. The story needs to have more twists or turns to make it replayable. I finished all of the playthroughs, not caring whether the NCR or the Legion took Hoover Dam. My companions were of no exception either. Boone didn't care about who lived or who died and Veronica left you if you even looked at the Brotherhood of Steel wrong. That's another thing: the story should not limit your companions at all. When I had to blow up the BoS bunker for the NCR, Veronica immediately left with all of my things. I didn't even get a speech check for trying to convince her otherwise. The story of Fallout 4 should be more open-ended, not just changing out the characters in the final scene.