1) Metacritic score means literally nothing, most of the critics on that website are SJW's who get offended by anything. Especially by Farcry 5 and its setting.
2) Why would you ever pre-order a Ubisoft title?
3) This game is still going to sell like a beast even if it's gameplay is more mediocre than Ghost Recon Wildlands.
Most of the reviews i've seen bashing the game spent one or two paragraphs talking about gameplay, and the rest were pretty much criticising it's political message and how it was handled. I'm not a big fan of Far Cry after 4 bored me out of my brain, but i've seen a lot of people having fun with, so i doubt it's a bad game. For those not tired of Ubisoft open-world tropes at least.
Still, 81 is not a bad score at all so in the end the good reviews are still outweighing the offended SJW.