The actor, who has played Sheriff Jim Hopper throughout the drama's entire run, attended the "Happy Sad Confused" podcast celebration at New York Comic Con Thursday and spoke about what's to come in the show's final installment ... including the series' last episode ever.

As David put it ... the series finale will be "the best episode [the Duffer Brothers have] ever done," sharing the cast broke out in tears during a recent read-through.

While David admitted he can be "very critical" of the show, given his closeness to the story and its characters, he promised the series finale will leave viewers satisfied.

He added ... "They land the plane ... The end of this episode when we were reading it -- just us reading it -- about halfway through, people started crying."

Per David, costar Noah Schnapp had the strongest reaction ... saying he was "uncontrollably crying" during the last 20 minutes of the read-through.

While this tidbit definitely makes us worried for Noah's character Will and his closest friends -- here's looking at you, Finn Wolfhard and Millie Bobby Brown -- David tried to brush off the emotional reaction as nostalgia ... since filming the show has lasted through much of the cast's entire childhoods.

He continued ... "It's 10 years later, and we examine that idea, and it's so well done and so beautiful ... It's such a great episode, and it's such a great season. You guys will love it."

Netflix has yet to release the season 5 premiere date ... but it's expected to come sometime next year.

BTW, with Noah apparently gettin' emotional, the question has to be asked ...