I love the original 1972, seen it many, many, many times.
SPOILER (Yeah, yeah, yeah, it's an old movie, but I still had a Star Trek plot ruined in this site even though it was "old", so this one's for you guys!)
It was the first time I saw a non-Superman film with Gene Hackman and was traumatized by the end.
I remember when I heard there was a sequel, I was hoping they'd find Hackman alive and well in the ship, but alas, they only found Peter Boyle, Jack Warden, and other actors.
What traumatized me in the original film was Roddy McDowall drowning halfway through. That bit wasn't in the MAD magazine parody so I didn't see it coming.
Having Slim Pickens outlive Karl Malden by five minutes was almost as traumatizing in the sequel. (We're only
told Malden dies.) Michael Caine survived, but BEYOND THE POSEIDON ADVENTURE's designated ''Borgnine'', Peter Boyle (the angriest guy) gets it at the two-thirds point. This was also Angela Cartwright's second, and last, major theatrical film.
I just Amazoned the BEYOND book which is also written by Paul Gallico, but it's done as a sequel to the first film's characters who made it, not the 14 survivors from his earlier novel. Only the three adult male survivors go back into the ship. I believe this follow-up book does in Jack Albertson's character.
The original novel kills off the young boy off-''camera.'' He vanishes and is never found. At the end the ship sinks.
Long ago this was my second favorite film ever. It's about 56th or 57th now.