IMO it’s actually ANH that’s the black sheep of the OT and not ROTJ. ESB and ROTJ both had much more more emotional depth then ANH which glossed over even a whole planet’s destruction with a population of millions to just be a fun space epic. ANH is still a great film but I’m willing to admit there’s some deep emotional depth not touched on in there, and dark stuff that doesn’t feel as dark as it really is because of the way it’s presented. You have an entire planet blown up full of millions of people glossed over, Leia doesn’t even have a scene where she grieves over it, Leia gets tortured and it doesn’t feel as dark as it should (compare with the similar scene in ESB with Vader and Han, in which you have dark music and hear Han’s painful screams), and Luke is stone cold when his best friend dies and there’s no mention of him afterwards. I will give it credit for Owen and Beru’s death, Luke mourning Obi-Wan and Obi-Wan recalling the fall of the Republic though (the looks on his face perfectly show that he’s been through some tragic stuff).
Plus it has no Imperial March, it was before Vader underwent his epic makeover (new shiny helmet, way cooler looking chest plate, actual chest lights, etc.; he didn’t look bad at all in ANH, he still looks awesome, but I feel like anybody who says they didn’t improve his look in ESB onwards is lying to themselves), it looks like its on less of a budget (which to be fair is because it was), in general aesthetic ESB and ROTJ look more alike then ANH does to ESB and ROTJ, ANH focuses a lot less on powerful Force users like the Jedi and Sith and more on more… I guess ordinary people? Like pilots, bounty hunters and politicians (ordinary is probably a bad word and an understatement but compared to Jedi and Sith they definitely feel ordinary). Which in and of itself isn’t a bad thing (I love the Mandalorian… a ton; I think its because of emotional depth, stunning atmosphere and great character development that I don’t mind the fact that its less about force users) but I like more balance. Now I’m not hating on ANH here, it’s got great story, character development, revolutionary special effects, excellent music, it’s a ton of fun, yada yada yada, but I’m just saying why ROTJ has more appeal to my modern sensibilities. I love movies that make me feel and think more, and the thing that interests me most about Star Wars is the Jedi and Sith and the powerful force users in the PT and OT.
I know people will bring up the Ewoks as a way of saying how ROTJ is supposedly way more kid friendly, but think about the heavy stuff in the stuff with Vader, Luke, Sidious, Yoda, and Obi-Wan. That scene with Luke and Vader on Endor with Luke telling his father to come with him is one of my favorite movie scenes of all time and incredibly powerful and deep. It’s a meaningful, beautiful conversation between a son and his father who went on the wrong path and let his rage consume him and lost everything he had ever loved, and his son is trying to help him out of the horrible trap he’s fallen into. When Vader says “It’s too late for me, son”, that shit hits hard because I know what it’s like to hate myself because I messed up and think it’s too late for me to dig myself out of a hole I’ve dug myself into. It’s emotional and deep and part of why Anakin Skywalker/Darth Vader is my favorite character of all time. Obi-Wan and Luke’s conversation on Dagobah is also very deep. Though I think someone said it’s because he was sick of doing the movies, Alec Guinness looking more tired and depressed actually works very well as he reminisces about Anakin and talks about how he’s “More machine then man.” And when Vader goes back to being Anakin and saves his son from the Emperor is my favorite movie scene of all time. It’s very dark and powerful. Luke’s screams for help are heart wrenching and when Anakin picks up the Emperor it feels so triumphant, and then it feels so touching when Luke goes over to his father and comforts him. Anakin’s death is also impactful and sad, I don’t cry but I almost do. The whole thing has the emotional depth of an ocean and it gives it the screen time and gravitas it deserves. The acting is utterly incredible and the character development is phenomenal and tugs at my heart.
Even think about some of the stuff at Jabba’s palace. You got sex slaves that are dropped to their death underneath a trap door where a monster will eat them if they are disobedient. If anything the Ewok stuff is there to balance the fact that everything else is so serious and dark. It’d be a very dour, dark film otherwise.
So yes, I’d say underrated. For me its ESB > ROTJ > ANH.