For me it's the quality of the NPCs that make all the difference. I'm not impressed with NPCs in Elite, so I welcome encounters with CMDRs, but over in Elder Scrolls Online I actually prefer having a delve all to myself. Eveli (an NPC) has started to feel more real than many players. Part of this is that a good NPC plays their role and feels part of the world, whereas another player often feels like just that - someone
playing a video game, rather than someone who is
part of the game. Too many humans turn Elder Scrolls Online into a theme park rather than an immersive world.
Now over in Elite, when I wing up with other players, I get an immersive bond that we just don't get from NPCs in Elite. Elite's NPCs are just autopilots with holome avatars and cheesy text lines. In Elite's case, players tend to make the game feel more real, except for certain gankers (pad-rammers, idiot children screaming profanities in the system chat, etc), and I just block those folk.
Regarding Star Citizen, I'm personally more interested in Squadron 42, because that game at least has the potential of offering meaningful, believable NPCs. If CIG puts as much energy into character narration and "humanity" systems as they do bed deformations, I'm sold!