To me, it's a combination of the story, the storytelling, voice acting and music. The graphics can help with the immersiveness of a game, but they're only secondary. The games I used to play as a kid like Monkey Island, Sam&Max and Full Throttle still hold up today, despite their dated graphics.

I bought an Xbox last year and a copy of Red Dead Redemption 2. It instantly brought me back, the same feelings and attachment to the main characters. I broke up a little when Arthur died.

I can appreciate the modern, realistic graphics but without the rest... it's just a technical fad. While the other way around you can still make a great, immersive gaming experience without realistic graphics.