It’s important to consider the kind of game that Dungeons & Dragons is to see why Stranger Things leans into it so heavily. It is the type of game where there can be two optimal strategies (throwing fireballs vs. casting protection spells), where people can do heroic things beyond mere human capability, and where players are constantly coming into contact with circumstances beyond their control. The ability for the player to think about, react to, or work around a problem in a freeform way is what makes tabletop roleplaying a fundamentally different experience from video games.
—  This Vice piece by Cameron Kunzelman neatly captures why the presence of D&D in Stranger Things isn’t just there as window dressing to let us know we’re in the 1980s. There’s a lot more to it.