These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Hype Backlash: The film is a perennial Cult Classic, but popular opinion has been steadily turning against it in recent years. There is much more adult-oriented animation available today than there was in the 1980s, and now that Heavy Metal has finally received a video release and it's no longer immensely difficult to find, everyone can see through the crappy writing, the mismanaged tone, and the needlessly gratuitous gore & nudity. That said, most people still agree that the soundtrack kicks ass.
MST3K Mantra: Since there were so many problems with production, the movie relies on the mantra a lot to make up for the plot holes and lack of continuity. As The Agony Booth pointed out, if a movie is so full of plot holes that you have to be completely stoned just to enjoy it, then it's not a good movie.
Nightmare Fuel: B-17. The shortest segment, but definitely the one that accomplishes its goal for the largest portion of the audience, and that goal is to be fucking terrifying. Whether it is the opening section where most of the bomber crew is killed in a difficult bombing run or the Zombie Apocalypse afterward is a matter of opinion.
They Just Didn't Care: For whatever reason, the final two scenes of "So Beautiful, So Dangerous" are hastily edited together in reverse order. In the final cut of the film, Gloria and the Robot get off the spaceship and walk onto one of the space station's escalatorsnote You can even hear a tiny bit of Elmer Bernstein's end-of-segment music a split second before "Heavy Metal" by Sammy Hagar kicks in, meaning they had it correct at one point in the editing process, followed by Zeke and Edsel landing the ship on the station. Once again, try not to think too hard about this.