I would divide it into acts and release them incrementally, possibly based on feedback and other factors that you really have no information prior to releasing the game.
Each act would have its own intro and conclusion, but they would fall within the main story.
If necessary, this provides me with the opportunity to go into more detail that I may have glossed over to avoid starting a project that was going to take years to finish if every part of the game had consistent amount of detail.
Who's going to play a game and then think "omg what a cash grab this is just one part of the series"?
Maybe when you've released all 3 games or something and then the people looking back on human history will go "oh wow this guy lol what is he doing"
But as far as I'm concerned, if I played a game, watched an intro, went through a series of events, and then reached an ending (which might be a cliff-hanger that leaves me wondering), I'm not going to immediately think "what a scam they should just release the whole game at once"
Because obviously I already knew as a player that the game was just the first part of a series.
Unless you mean you're going to explicitly tell your fanbase what you're doing.
When the second game comes out, some people may draw some connections and may suggest that you've broken up a single game into multiple parts, but really, this seems like an advantage: you can add new systems, remove features that weren't very popular, introduce new characters, change your database around, etc.
And of course, it's a NEW GAME. You can charge full price for this. It's not an "expansion" or a "DLC" or anything. Sure, same characters, same universe. What's the problem?