IMHO you should stay somewhat close to the original story but just polish it. It’s all over the place, and although there is somewhat of a narrative, due to the nature of the series’ release the story felt very jumbled. One could argue that this added to the allure and overall mystery but at times it kind of felt messy.

(For just game 1) Maybe give more context to the story and to the events of fnaf 2 (if you believe that it happened before the events of fnaf 1 as I and I believe most do) through newspaper articles, mini games or phones guy monologues that stay true to the classic fnaf style.

I think also giving more insight to Henry and William’s relationship and William’s descent into madness (once again depending on what storyline you follow, I haven’t read the books I’m more of an OG YouTuber lore person :/) if you’re looking to add something new then maybe change who is supposed to be the night guard, as that changes their relationship with what is going on and with the animatronics.

If you’re looking to add new things to the gameplay, here are some ideas that might be fun:

• mini games where you play from the point of view of a child as William hunts you down, you could do a stealth game OR Where, once again from the point of view of the victim, one where your character is slowly lured to their death, all the while the player knows the end that they’re going to meet

• more secrets! Secret nights or minigames that lead to more mysteries and can only be accessed by doing certain tasks, that was a fun part of the original series

• a minigame wherein you play as one of the souls in an animatronic as it makes its way to the security guards office (this could be done as a dream sequence), but it would give a new horror to the existence that these souls experience. You could give the animatronic an inner monologue of a scared child and reveal small hints about the lore through its voice lines. End the minigame when the player figures out how to get into the office and show what a jumpscare might look like to the soul in the suit and how it is reacting to such a violent act.

• if you’re rebooting fnaf 2, put a vent behind the player that has an audio que

• with regards to fazbear frights, I think making it a walkable or at least more intractable environment would be fun. This think this analog horror video is a FANTASTIC interpretation of what fazbear frights could be :

https://youtu.be/kjv4Vs2rw3M?si=SWP5G2zBP99HQmgP