So when I was still playing through Route A, I lurked these forums and read a lot of stuff like "don't judge this game until you get to Route C" or "Route C is the best part" and I have to say that as emotionally charged as Route C is, it's extremely flawed gameplay-wise and is not the defining part.
The first real bit of gameplay in Route C is when you start hacking the defense systems in City Ruins as 9S. What a horrible way to start the player off. Unlike most people, I enjoyed the hacking in Route B but even I found this early part in Route C dull and meaningless. Hacking was always fun to me when it was a challenge but when it's a trivial task like at the start of Route C, it's just a waste of time. Also, the designers didn't think that perhaps the player had already done enough hacking? There's no reason for this segment of the game to exist.
Taking control of the City Ruins as 2B is okay, I guess. All you're really doing is going through old parts of the map and fighting machines while protecting your own YoRHa units. It's not as monotonous as the previous part and it has more obvious purpose but it's also not that exciting.
The next part is probably the most interesting part of Route C. Your own YoRHa units become contaminated with the virus and you're pitted against them. It feels completely different to fight these guys. Their attacks are not nearly as telegraphed as the machines you're used to fighting yet they should be familiar to you. The Bunker which you previously knew as a save haven suddenly becomes the next arena for your battles. This is actually a pretty exciting part of the game.
Up next is probably the most frustrating part in the entire game. 2B finds herself contaminated and must move from point A to B... only most of the time, you aren't allowed to run or jump. Is it a fun scene in the story? No. Clearly, it's not supposed to be very enjoyable but maybe there was also no need to make the player suffer through something so annoying either? Maybe this scene and 2B's eventual death could have been all done through cutscene. The lack of checkpoints in this part is pretty frustrating too. If you fail, you have to restart all the way from The Bunker.
9S's parts... You go through three nearly identical looking Resource Units. The first one is basic rooms of enemy machines. The second one is more monotonous hacking. The third one is kind of a combination of both. Very repetitive stuff.
A2's parts... You run through the desert and there's a giant boss to fight without much of anything interesting on your way there. It's okay but the level/encounter design here isn't creative or anything. Then A2 meets Pascal and these parts are passable. When the village is attacked though, it's clear that the Machine Village wasn't designed with combat encounters in mind. It's just not a very dynamic place to fight. The only other notable thing here is the Goliath vs. Goliath fight as Pascal but as much as it offers spectacle, it's all very slow paced and boring.
Then, finally the Tower stuff. Ko-Shi and Ro-Shi are pretty cool, I won't lie. The last hacking minigames you did as 9S against A2 were pretty creative. The final battle as A2 against 9S however felt like annoying bulls***. Overall, the game became more engaging for me gameplay-wise in these last parts though.
Tl;dr Route C is just not very fun/engaging.
And I know someone's going to say "lol you want gameplay in a Yoko Taro game?" but before you type that, remember that this is both Yoko Taro and Platinum Games.
If you ask me, Route C is not the defining part of Nier Automata. Route A is the main campaign, Route B is the same thing but from 9S's perspective, and Route C is like a bonus story with a new beginning, middle and end. It's almost like Nier Automata 2. It felt like a bit of a drag for me to play through though and I feel it was overhyped.
