I almost feel bad for not enjoying this mission, because it's bloody beautiful. I mean it, the architecture and atmosphere are phenomenal. The problem is this mission quickly becomes a slog of a key hunt. And there's platforming. The twist and the way it's executed when you think you're about to grab the McGuffin is really well done, but the rest of it is a lot of backtracking and retracing your steps, which wouldn't be so bad if it felt organic. But there are doors that will only open a crack, and then doors that won't open at all, and maybe 2 you can pick open. It's frustrating because it plays more like an adventure game than a thief mission, which is fine if that's what you're into. If that's your bag, you'll find this mission to be a ten.

And it does have genuinely creative elements, and one of the most crazy complex puzzles I've ever seen.
If you're giving it a go, then explore literally everything every time you open a new area. Every tiny nook and cranny, and take extensive notes.
And don't forget to admire the atmosphere, the architecture, and the beautiful execution of this level.