I have yet to beat the game (125 hours in so far) but am simply loving it. I have seen lots of hate about this mission, so i created an account just to give my constructive opinion.
Seriously, the mission was brilliant, it was like a game (Prisioners of War?) inside a bigger game. Loved the fact we had no resources (lockpics money, etc), the fact there were lots of side quests and activities inside that place, misteries to solve, a schedule to follow, the fact we had to pretend to be a monk during the day, and act like a thief during the night in such a limited area, and of course (this one has to do with the fantastic job Warhorse did with a seamless world with lack of loadings between in and out doors) how you could look outside through windows and see the forbiden outside world.
I love KCD, but this quest was a great change of pacing for me.
On the down side, the schedule and routines of everyone inside end once you finish the mission (at least happened to me). Once i finished it, i went back to the monastery to explore some doors and chests i didn’t before, abd realised that every monk was always in the dinner area, no matter the time of the day. That killed the immersion a bit, but then again, i’m sure devs will fix it soon.