Personal pet hate: series that all end in exactly (or almost exactly) the same way. It’s a real problem because it’s hard to give them meaningful differences without making it hard to continue the next one.
Couple of suggestions: Make it a difference that can be fairly resolvable before the next one by including a decent epilogue. For example you have a series of events that can be wrapped up in a scene but still provide a different ending. For example if you had a superhero type story, perhaps the MC was badly injured in the final battle for one ending and has to spend time in hospital recovering which takes a toll on the public’s perception of them since they seem to have gone MIA, in another ending they come out of it relatively unscathed, get all the acolades etc. By the time the next sequel comes around, they can be healed up and ready to go, but you could have some variable and stat changes remaining to remind the player of what happened last time without it derailing your next part.
Another option would be to have things happen that matter to the story at hand, but not so much to the next one in a episode like format.
Or you could have interchangeable type differences. For example if the hero saves a minor character, they reappear in the second book in some fashion, if they don’t, it’s a replaceable “similar but new” one.
Anyway, just my 2c. May not really matter since it seems as if many people don’t replay games anyway so I don’t know how much railroaded endings bother the main population of readers. I’d certainly go there, rather than make it an “only selected endings get a sequel.” IMO that’s asking for angry reviews from people who feel like “their” story hasn’t been written an ending.
(Edit: IMO each game in a series should ideally be able to stand on its own, so you get a conclusion at the end of the first book, then the story starts up again and adds to the first in the second rather than leaving things feeling incomplete. That’s where I think epilogues or a conclusion chapter of some description can really help round things out, and then in turn allow the next book to start off again without too many problems unless you’ve allowed the story to branch too far afield.)
Someone’s been watching GOT I see