Oftenly considered the weakest in the series by a bunch of players and specially fans, Five Nights at Freddy's 3 is on this weird limbo where it feels like it didn't achieve what the first 2 games had, thus winning over the players with a general consensus that they are 2 very great games. You do not see that as much with Five Nights at Freddy's 3.

This series is full of little games, so it doesn't contain the same substance as your usual games, but somehow it feels like they are packed with new ways to impress the players and give a new and different experience.
Five Nights at Freddy's 1 is more simply and straight forward, where you are focused on tracking down positions for the animatronics.
Five Nights at Freddy's 2 is about keeps you on a rhythm on how to do things while making sure you get used to quick and swift events.
Five Nights at Freddy's 3 may not seem like a lot at first but when you go deep down you know understand how brilliant some of its game design is done. I want to focus more on this game design to understand what makes Five Nights at Freddy's 3 stand out. But first I wanna say, this game is by no means perfect, and it does have... weird issues.

I gotta say I love the gameplay loop for this game, the other 2 games may have it weaker due to how it can be much simplified with a few strategies, this is the point where both of the first games stop losing the "free-style" of what Five Nights at Freddy's 3 maintains, and nothing represents free-style more than Springtrap and the Phantom animatronics.
Springtrap has to be one of the best designed enemies in the series, being this one enemy that can kill you, and it is also one of the only animatronics that sort of changes what it wants to do. Will they take a longer path? Will they go through the vents? Will they go backwards on their own? Will they listen to this audio cue?
All of this is important to track the main enemy with the best use of the cameras in the series; cameras are a mixed-bag in the series because of this strategic feel of the first 2 games, with the third game making sure every camera is important.

In addition to Springtrap there is also the control panel, having 3 errors you can manually fix, adding risk/reward to the mix. In order to fix these you can select the error you want to fix, which takes a few seconds to complete, or fix them all which takes a bigger amount of time, allowing for Springtrap to speed up or go through a vent at an unfortunate time. This really allows Springtrap to be an excellent, dangerous and unpredictable threat you should fear. Blocking your camera vision, disabling your audio cues, and/or breaking the ventilation system comes with a lot of drawbacks and are an important priority for dealing with Springtrap

Springtrap does feel like an actual threat when you have to keep track of a lot to make sure he doesnt end your run. But the thing is, he isn't alone in this.
Phantom animatronics are also here as little threats to make sure the job is more difficult to do. Almost all of these phantom animatronics are unpredictable so you have to adapt accordingly with the situation or they could potentially make Springtrap get too close for you since they do not kill the player, but it allows the player to recover from that situation they are in.
Phantom animatronics don't kill you but they work to make sure Springtrap gets close, almost like little minions that are not THAT big of a threat but there is then the king that may seem easy to deal with but in combination with it's minions it can be a powerful combo. And thus, what makes it seem like a simply game turns into a constant worry about all of these systems to make sure you do not survive.

I think this is genius and they all feel so well thought out and planned to create a much more different but distinct experience compared to the other games, and it allows the more "free-style" aspect to shine, because you are adapting so much with so many threats to make sure the main threat doesn't end your run, that to me is amazing gameplay design.

However, this game at the same time is... weird. Because it does a few things the first 2 games did a bit strangely.
Like for example Night 1, which I do not understand the reasoning for being a nothing night, I can maybe see this for like a testing-ground night, but making it have no threats is definitely a strange decision.
There is also the lack of a Custom Night and I think that's a big shame because this game can really benefit from one, and even if the Extras are a new thing, they do not add much to the experience of adding a replayability and custom-like feel.
Nightmare Night is here which is nice, but the game does fall a bit short on nights compared to the other games, which honestly is my biggest problem with this game.

Outside of those, this game is a blast that looks really good, plays really well, has a lot of easter eggs and interesting ideas, has minigames that do a well enough job of explaining lore, and these can be broken apart to reveal even more secrets to get the Good Ending.
I won't deny, this game is by no means perfect but I do feel it gets beaten down a bit for what it is, what it is is unique, fun and intriguing!
Weird game but great game!