I first saw this movie around the time it came out on DVD and didn't remember much more than despising it partly for its pointlessness, "we just blew up your world, here's another one" but also because of that idiotic scene with the "View Gun" (a gun that causes the person shot by it to instantly see things through the perspective of the shooter), with every shot the person shot would suddenly begin stating a very obvious argument for the other person but still very rhetorically weak and even while watching it I could think of rebuttals for each one but the cream of the crop from this scene was when Zaphod (the guy who was being shot by the gun over and over, he also literally had half a brain at this point so I really don't see how the writers thought they would justify the anger against him, oh yeah they didn't) snatched the View Gun, pointed it at Trillian and he decides against even trying the gun when she says "It's not going to work, I'm already a woman," if another actress had said this, I may have not cared or even thought it funny as I'm guessing I was supposed to do but at this point, whoever was playing Trillian had already earned my despise and she did it in her first few lines of the movie. She was meant to play the smart, attractive girl in the movie but somehow she came off as seeming like a really dumb actress trying to remember the long words from the script so the techno babble would make her sound smart and that's probably what she is.
To prove I'm not enraged solely by the movie's deviance from the original story, I'll begin with the beginning that followed the book nearly verbatim albeit for a few details but I've never seen a director so masterfully sabotage a film. Rather than play out the entire opening, the scene in the bar was replaced with a flashback of how Arthur met Ford Prefect, skipping the part of Ford convincing the bar that he's serious about the world ending (they just take every apocalypse theory at face value apparently), him getting everybody at the pub mad at him by constantly smiling in a very creepy manner and even before the pub, and before any of that, a great foreshadowing scene with the bulldozer (yes, it was there but it was reduced to the bare minimum). Apparently the movie would be too long if they added in those three pages of dialogue and came close to actual character development because they needed to throw in visits two other planets that never occurred in the book because the movie had magically become too short.
When the Vogons arrive to destroy Earth the movie still seems to be staying true to the book but again, just a few details taken out ruin the whole thing. The Vogons speak into a microphone and are heard throughout the Earth but they skip the chance to add a potentially really cool scene to show how everything from record players to trash cans to everything you can think of that can generate sound become speakers for the Vogons. A few seconds after their announcement, it's implied that somebody uses a ham radio to plead with the Vogons to spare Earth, but in the movie they not only don't have a voice-over of such a plead of desperation but the Vogon about to destroy Earth instantly begins his (or her, who knows) rebuttal far too quickly for the theater to even think somebody may have made contact, so in theaters it simply seems like a poorly acted script.
In the Vogon ship, several scenes are omitted from entry into the movie (again, probably to make room for the two extra planets that are absolutely necessary because the movie would otherwise be too short) such as Ford explaining how and why they were picked up by the Vogons who hated hitchhikers, Ford constantly telling Arthur to quit whining about his planet (Ford's was blown up around the time of his birth and he was the last of his species but this is not only not mentioned in the movie but it would be difficult to convince an audience that it's true based on Ford's far too cheerful character alone) and Arthur's breakdown over The Hitchhiker's Guide's lacking entry of Earth believing that once he's thrown out into space all that will be remembered of his planet, country, life or anything would be a description of "mostly harmless."
Once Ford and Arthur are picked up by The Heart of Gold ship the very entry into the ship is a perfect example of how the movie begins to move away from the book and even fails to incorporate my favorite line from the book ("Ford, you're turning into a penguin. Stop it!"). The trips to the planet with the five-armed aliens and the Vogon home world don't exist in the book (the five-armed aliens aren't even mentioned in fact) nor are Zaphod's heads ever separated, is the View Gun mentioned or do the Vogons ever make another appearance after Earth which would've made the ending far better if they had stuck to the methane breathing aliens that were threatening to shoot Zaphod (oh yeah, the presidential kidnap thing was Hollywood's idea as well, he was in pursuit for stealing the ship) but my point is that the differences just became greater and greater as the movie went on and while I thought the eyeless, legless politician was an interesting character, he introduced a very unnecessary twist that winds up never being resolved in the end of the movie and even if a sequel were to be released (as they have for the books) this unnecessary twist does some serious damage to the rest of the story and sorry, but I must yet again contrast the movie and book.
Soon after picking up Ford and Arthur, Zaphod says "after seeing this is when I realized I had to do what I did to my brain," naturally referring to slicing it in half and putting one half in each head according to the script but to the book which not only had the two heads as natural and fully functional (probably, they were never separated in the book) but a certain part of each one was wired to only communicate with the closed off part of the other brain. The book went into much more detail about how he got the surgery past the government tests required to become president and even how he figured it out himself but the books had a sense of anticipation, which is one reason why I wouldn't give them the harsh review I'm giving this movie.
In the long run, this movie doesn't even feel like an adaptation. It feels like a normal movie that is so laden with references to the book that it borders on completely unoriginal and ironically, a completely unoriginal, true-to-the-book adaptation (not every detail, just the main points) would have been far, far better than this, from the scene with the mice trying to take Arthur's brain to the fights over whether or not Magrathea is real to the final shoot-out, it's as if the director chose the worst scenes to cut at every possible junction.