The Poseidon Adventure was the film that established the basic conventions of the disaster genre, i.e. a group of A-list stars in peril. In this case, they're guests on a luxury liner which is capsized by a tidal wave.
I'd seen Shelley Winters in earlier films, especially Lolita, and I was surprised by how much weight she'd put on by 1972 (when The Poseidon Adventure was made). Even more surprising was what she was put through during the film - she appears caked in grime, she has to swim underwater, and she is constantly criticised for her weight. I've read previously that she was a very stroppy actress, so God knows how she was persuaded to do half of the things she does in Poseidon.
The part we liked the most was after Gene Hackman, the lead actor, has climbed the Christmas tree. Everyone was on the floor (actually the roof, as the ship was upside-down), and Hackman realised that if they propped up a large Christmas tree they could climb up it and reach a ledge that led to a potential exit. He convinced a small group to climb up, but most people wouldn't listen to him. He tried one last time to make them see sense, but they still ignored him. So he climbed up the tree himself, and, from the ledge, he paused to look down contemptibly at them. Then there was an explosion, and the scene below him suddenly looked like Sodom and Gomorrah in hell - a writhing mass of burning people. Hackman turned his back on them and went through a door to safety... and then he closed the door behind him!
It's one thing to turn his back on them, but closing the door on them as well seems a bit harsh. Hackman's character is a priest, after all. It's a very funny moment, though, and the film is worth seeing despite most of the acting (apart from Winters and Hackman) being a bit ropey. It also has Leslie Nielsen as a deadpan ship's captain at the start, so you think it's going to be a parody but in fact it isn't (not intentionally, anyway).