It’s interesting to consider how video games do differ from literature, film, and other storytelling mediums when it comes to sequels. Good film sequels are an anomaly, but video game sequels… well, there’s plenty of terrible ones, certainly, but mechanical improvements often mean even a disappointing story can be mitigated with gameplay. I love Dragon Age II’s characters and setting, and I think the writing in Inquisition is quite dreadful and lifeless, but by god is Inquisition much more enjoyable to actually play than II.
I think my favorite game that is a sequel, regardless of its merits as a sequel, is Elder Scrolls III: Morrowind. It’s very different from its predecessors, in some ways I even find myself wishing we had a branching timeline to peak into of an Elder Scrolls series that stuck more to the first two’s style, but as its own thing? Morrowind is a pretty near perfect game. Absolutely adore it.
Fire Emblem: Path of Radiance, Fallout: New Vegas, Final Fantasy IX, Mother 3, Kirby: Planet Robobot, The Legend of Zelda: The Wind Waker, Dark Cloud 2, Crusader Kings II, Knights of the Old Republic II, and Castlevania: Symphony of the Night also all deserve big shout-outs for that category. And since the series came up earlier in the thread, I will always have a fondness for Assassin’s Creed Syndicate.
Wolfenstein II: The New Colossus, honestly, might be my favorite sequel that is entirely, narratively a sequel to its predecessor. Great development for BJ and some of the recurring characters, plus several stellar additions to the cast - Horton and Grace, especially. Kingdom Hearts II definitely deserves a nod for being one of the best follow-ups to its predecessor both narratively and mechanically.
And it’s not done enough to know how, exactly, it is a sequel to Undertale, but I suspect deltarune is going to be a contender one day.