Adaptation Displacement: Not so severe as some examples, but the book is much less famous than the film.
Awesome Music: "The Morning After" is a song winning Best Original Song at the 45th Academy Awards. Meanwhile, the one and only John Williams provided the score.
Ensemble Dark Horse: Martin and Belle. Martin for his great Character Development into the competent and level-headed voice of reason of the group, and Belle for her memorable swimming scene where she saves Reverend Scott's life.
First Installment Wins: Granted, many people don't even know Beyond the Poseidon Adventure exists. And those who've seen it deem it an outstanding piece of Sequelitis.
Funny Moments: Early on, Robin fights with Susan and says "Shove it!". Susan tells him never to talk like that to her, prompting him to say "Shove it shove it shove it!".
Seasick Linda Rogo is given a suppository to aid her. Mike Rogo loudly complains it's too big to swallow, and is confused when the nurse tells him it's not to be swallowed. Linda has to tell him, "For Christ's sake I know what to do with suppositories! Just get them outta here!"
Scott tells Linda she can't climb the tree in her gown and she has to take it off. Rogo protests that she has nothing under it, leading to Linda's iconic line, "Just panties. What else do I need?" When Scott tells Rogo to give Linda his shirt, Rogo's reaction is priceless as well. "Ohhh Linda. Next time you put somethin' on like I told ya ta put on."
Scott then tells Rogo to help Linda up the tree and follow. Rogo, irritated, loudly asks if Scott ever says please. Scott's reply? "If it will get you up that tree...PLEASE."
Martin asks Rogo what they'll do if Scott doesn't return from examining the ship's kitchen. Rogo's reply? "Tell 'em to break out their hymnals and start singin' 'Nearer My God To Thee.'"
Rogo's grumbling the more Scott orders him around. "Yeah, Rogo, Rogo, Rogo." "Figures, it's me again."
Linda's rip off the bandaid approach when they're trying to move to the next deck and Nonnie sees the incoming water and starts panicking and screaming. "SHUT UP! Get up the GOD DAMN RAMP!"
Hilarious in Hindsight: Leslie Nielsen playing it straight as the captain of the Poseidon in a disaster movie, seven years before Airplane!, a spoof of disaster movies. The Syndrome was still a decade away. In fact, it was because of his performance here that he was approached to audition for Airplane!.
Karmic Overkill: Linda Rogo is often insulting, and a bit of a Jerkass, but ultimately she does try to help and offer support, albeit not in overt ways, and for the most part, does the right thing. Still, that doesn't stop her from being coldly killed off less than 10 minutes from the end, AFTER Mike Rogo has begrudgingly admitted Rev. Scott was right, and AFTER they get within visual distance of the propeller shaft they've spent the majority of the film trying to reach. Mike REALLY doesn't take it well.
Narm: Belle's death, to the point Bette Midler made fun of it in her act.
Nightmare Fuel: The guy who falls into the ceiling light.
Not to mention the aftermath of the capsizing. You're on the ceiling of a party room. If you were lucky enough to remain uninjured, you're hearing the pitiful cries of those that are, and you're walking among a ceiling littered with corpses of people in fancy evening dress, and the room only has limited emergency lighting for you to see through as well.
If you're one of the people that refused to leave with Scott's group, congratulations. You're either going to immediately drown, or swim as the water rises with nowhere to go until the room entirely fills with water and you drown a little while later. Even if you rise with the water level and try to follow the path you watched Scott's group take, the water is going to overtake you. All three of your options are drowning. If you're with Scott's group, you have to live with the fact that there's nothing you can do to help the others, and walk away from them as they scream for your help.
Being one of a handful of survivors on an upside down ship. Especially because the ship is not designed to float upside down. the weight of the water is literally pulling the ship down as you go up, because the upper decks of the ship are not equipped with the watertight systems that would be in place if the hull was breached. You're completely gambling on making it to the hull above the waterline. You have no idea if the ship will pull an Andrea Doria, which is lampshaded in the film and remained afloat for hours after it was opened to the sea, or a Lusitainia, which sank in 15 minutes, or even a Titanic which lasted around two hours. You have emergency lighting to see, but you don't know how long it will last. Everything is now upside down, so traversing anywhere is treacherous. Can't swim? Have fun having to go through a flooded passageway to get where you need to go. The worst part? You don't know if a distress signal was sent and if anyone even knows the ship is in distress. When you get to where you want to go, you won't even know if anyone is there to rescue you, or if you're going to drown in the dark, trapped behind an inch of steel when the ship finally sinks.
Tying into the above, all of the senior crew is dead. You're in a situation that no one could ever prepare you for, and there's no heroic captain or senior officers to lead you or guide you. Any emergency or lifeboat drills you've participated in up to now are completely moot. You're stuck getting advice from an out of his depth purser who happened to be at a party, or if you're lucky, you manage to find a living steward who has some basic understanding of the ship that can point you in the right direction, or one of the passengers who was fortunate enough to get a tour of the engine room. In any case, you're in unfamiliar territory and are reduced to fending for yourself for even a limited shot of rescue.
Finally, the water is following you. No matter where you end up, eventually, it's going to catch up to you. If you're afraid of drowning, or have a fear of water, you're probably seeing a lot of yourself in Nonnie.
Harsher in Hindsight: A tsunami that kills a lot of people on Boxing Day? Needless to say, it's even more horrifying after 2004...
Values Dissonance: The whole "Susan getting raped" subplot, full stop. Not only is the attack itself completely superfluous to the plot, but her subsequent reaction to it (she sympathizes with her attacker, to the point of mourning his death, planning to meet his parents after getting rescued, and hoping she's carrying his rape-child) could only be the product of a male author from a pre-feminist generation.
...