The Mad Max films are pretty unique as far as trilogies go: each film is completely insular, existing as a self contained work of art, but when they are viewed together they also tell a complete story. In the first film we see society crumble through the eyes of a cop named Max; in the second film we see how everyone is trying to adapt to life after the apocalypse; and in the trilogy's finale we see how society is reborn through the eyes of a new generation of kids. Because the only consistent character is Max and because the narrative through line is metaphorical, not literal, the films don't have to directly reference each other, but they also make more sense when viewed as a whole, rather than stand alone entries in a series.
The problem with the third entry into the series, however, is that it I'm not sure that the series should end on an optimistic note. There are a lot of thrilling stories about heroes who manage to stop the end of the world in the nick of time, and there are plenty of bleak stories about people trying to survive in post-apocalyptic wastelands, but films that try to mix those two tones are rare.
There's a good reason for that: the transition between the fundamentally pessimistic tone of post-apocalyptic movies towards the fundamentally optimistic tone of a renewal story is just about impossible to do well. The stories are trying to accomplish vastly different things: one is about trying to create a penitent tone where the audience is supposed to think about what we could lose and the other is trying to create a more expectant tone where the audience is supposed to be reminded to treasure what they still have; on some level doing both at once is trying to have your cake and eat it too.
Perhaps this would be a less of a glaring problem for Mad Max Beyond Thunderdome if it wasn't structured so badly, but the film is bifurcated almost exactly in the middle, with the first half being an extension of the dark world of The Road Warrior and the second half entering a brand new world that feels like a steampunk version of Peter Pan. Because the shift between the grittiness of the adult world and the brightness of the kids' world is so sudden (and so narratively random; the kids just show up unheralded) it doesn't feel like the two parts belong to the same story. Both halves could make for an entertaining movie, but thrown together they barely make sense.
I understand why Mad Max Beyond Thunderdome ends the way it does: it pays off some of the threads of the first film, and the movie fits in with the 80's "Morning in America" zeitgeist in the same way that the first Mad Max fit into the late 70's "clusterfuck of paranoia" zeitgeist. But that doesn't mean that it's a good ending for the series. We don't go into apocalyptic thrillers because we want hope for the future - we go in expecting to explore our fears in a controlled environment. The first two films do a good job of that by showing how civilization could collapse and life would still go on. Mad Max Beyond Thunderdome tries to start at that dark place before moving beyond it, but that feels like a bait and switch. It's seemingly well adjusted teens feel like a contrivance in films that had for the most part done a good job of balancing being outlandish with being realistic.
Perhaps it's best that the series is made up of films that can mostly stand alone. If Mad Max Beyond Thunderdome has to live up the legacy left by the awesome Road Warrior, well, its going to be a bit of a letdown. But judged on it's own it isn't a bad film, really. The half of the film that takes place in Bartertown is full of cool ideas and the fight in the Thunderdome is a lot of fun. The second half of the film is less consistent, but it does make plenty of time for the sort of insane chase scenes that are the series calling card. It might be a bit uneven - but come on, it's life after the apocalypse. Expecting consistency is a bit insane.