For a vertical mission like this I didn't do much climbing, tbh. It's more like a long spiralling street, that goes higher and higher to the mansion, and it's quite linear. While the main objective is straight forward, with a few nice twists and spooks, the optional stuff was brutal. I don't have many points in perception, so it took me ages to find the necessary items. Nicely hidden. Water cascade is a nice fast travel tool. The mansion is a marble castle, but, thankfully, guards aren't frequent.

Visuals are great and atmospheric. Beautiful night quarter with great architecture. But the most impressive thing visuals-wise is a big spoiler.

SPOILER
Fun little things.
1) Since Thief community cracked the Horse Engine (tm), here we got guard dogs! Lovely. Hitbox is rather strange, though.
2) At first I thought I need to throw the letter into fire. I tried various fire sources and failed. So then I tried water and it worked. Not as reliable.

Now that you say it, yeah, the hitbox of the dogs is really pretty strange. Kinda like with burricks, just even more small/low.

At least they don't notice you from 2 kilometres away, like real dogs...

TBH, I found them a bit expendable though. Not my cup of tea, and, I don't really see the point.

Hey there. Throwing the letter in the fire should work, as it's one of the ways to destroy the invitation. It sometimes takes a second or two before it burns, though. It should work if you drop it in fireplaces or use a fire arrow.