Also, I don't even agree with the assertion that New Vegas is that different from games like Mass Effect 2 in terms of investment. I liked the companions in New Vegas. I couldn't ever kill Cass and I've never been able to sell Arcade into slavery. They're that likable. And Lonesome Road made me like a robot who can't speak. Maybe New Vegas feels more detached because you can go off the rails and kill whoever you like, but that's a point to its favor in my eyes. After all, it's an RPG. Mass Effect hand holds you so hard that it sometimes gets annoying, and as the series when on most of the choices you could make boiled down to "nice guy vs complete jackass". Even then, I often never had problems doing renegade interrupts to kill people in hilarious ways, so I couldn't have been too invested. You could reload if you didn't like it, too.
There are exceptions to that rule. I'm mostly referring to the 'regular' NPC's. What I really mean to say is that there's absolutely no narrative consequences for killing everyone you come across who isn't directly involved with the main quest, or a major NPC in their own right. You can kill everyone in Novac, and nobody anywhere else will care. In Fallout 1 and 2, killing people was a very big thing that had immediate and serious ramifications. In the towns where you could go an appreciable murder-spree without consequence, the lore always supported those actions.
The Den for example was a wretched hive with zero law enforcement and a population of slavers and junkies that nobody else really cared about, so killing people there logically didn't have many consequences. I prefer the karma system in this one respect, because it could serve adequately in the role of general reputation meter. There was a sense that your actions were always impacting a broader Wasteland, even in very subtle ways.
While New Vegas does have
some of that going on, it's not well-integrated or immersive at all. It's always very basic 'if you shoot X in the face, Y will have one additional line of dialogue, and Z will charge you more for fusion batteries' style cause-and-effect scripting that is transparent for what it is. The isometric games did a much better job of making reactions to your deeds organic and not making it obvious when you've triggered a script prompt.
Another thing is that the gameplay has a ton of issues that take me right out of it. The lack of NPC functionality is a major one, and is something I've come to find Obsidian as a whole has a problem with as well. As mentioned, you can murder every NCR trooper in a base and arrange their corpses right in front of their commander, and he won't even acknowledge them. This total lack of even a concession to reality is what takes me out of the immersive experience
hard. You're never penalized unless you do very specific things the game is programmed to consider 'naughty', and those actions are disconnected and deeply unrealistic.
I had a similar experience with Pillars of Eternity. Early on there's a quest where you get to choose between supporting two people who both have a legitimate claim to leadership of the starting town you end up in after the introduction. The sitting lord is a bloodthirsty knight Templar who has been systematically murdering large numbers of his subjects out of a misguided sense of justice. The claimant is a sleazy politician guy who is up front about just being in it for the position. I decided very quickly that I hated the pair of them and didn't want either in charge. So after infiltrating the sitting lord's castle and killing him, I went and collected my reward from the claimant, then killed him as well.
The game, despite touting itself as having an extreme dedication towards the narrative, had no answer to this. I went back to town and chatted with everyone, and nobody even acknowledged my choice. I played for a couple more hours after this, but in the end I just quit. I couldn't get over that basic lack of reaction to my choices that Fallout 1 and 2 would've taken and run with all the way to the endgame.
