Details are important. It's the small things that flesh out the experience.
For example, for me, when your companions stand there like paper dolls with a thousand mile stare, it bothers me. I want them to look at me. Turn their gaze to other npc's when they're talking, etc. That kind of thing makes these pixel bags feel more present and alive. When they're like paper dolls, it ever so slightly pulls me out of the experience.
Details in the environment. The art. I notice these things, and I appreciate them immensely.
One of the things I liked about the Citadel dlc was that it had more details. Like when you're picking your crew and one/some of the other squaddies remark, "It seems I rarely get picked." I was caught off guard with that because I knew it was true. There are certain squaddies I predominantly roll with. So it was funny to me that they recognized that. I liked it.
I liked it when I was shooting my way outta the Citadel...shopping area...and I come across a fruit stand with a sticky note that says, "I know you've been licking the fruit when I'm not here. Stop." Me: "Whaaat?"
A few glitches I can deal with here and there. As long as they're not persistent and a pain in the azz. But details in environment. Details in story, and the story remembering them. Details in character interaction.
Things that, yeah, maybe alot of players might run by and never notice, so why be bothered. But when that detail is there to be discovered, and you do discover it, it's pretty cool.