You fell in love with a game and it’s characters, sunk hundreds, maybe even thousands of hours into it. It became a comforting, immensely satisfying part of your daily life. Then you heard a sequel was coming and got really hyped but when it came out it was utter rubbish…
Which game(s) was that for you?
I don’t think it would be possible for a bad sequel to ruin a game I liked.
Metroid Other M has not ruined previous Metroids for me (its terrible Adam Malkovich depiction doesn’t even register when I’m playing Fusion, since the character has barely any continuity between the two).
Okamiden did not ruin Okami, it just sucked on its own and what little story it tried to change I disregard. I’d replay Okami today in a heartbeat.
Xenoblade Chronicles 2 took a direction I hated, both in style and gameplay, and it made me want to replay XC1. I did. It’s still awesome, though XC3 became my favourite.
And complete opposite of the topic : Baten Kaitos was not bad, but kind of a silly popcorn game to me. Baten Kaitos Origins did not ruin this game : it was so great and flipped the interpretation of the first game so well it made BK better.
You’re right that it’s hard for a sequel to retroactively ruin a singleplayer game, but they can easily ruin a multiplayer game by killing the original’s playerbase.
There are also plenty of cases where the sequel may not ruin the original, but does ruin any future the series could’ve had. Debatable whether that quite fits OP’s question, but it seems to be what most of the replies have talked about.
Well, I did say a sequel would probably not ruin a game I liked… And admittedly, yeah, this involves very few competitive multiplayer games.
The part about a beloved franchise or character didn’t really evoke that kind of ruining to me. But I get that point of view.