Well, I´m kinda in a dispute how to review mission.
At first: It´s really difficult. If you are into that, then just go ahead.
But if you are looking for a a rather relaxing mission, you should really consider if you should give it a try or not.
Because the biggest frustration factor is the loot goal. There is a total of 8400. I ended up with around 5600 and for some of the objects I had to view spoilers because I wasn´t able to get the needed 4500 for expert otherwise. Honestly I have no idea where the rest is. Ok, I know it somehow as thankfully someone made a loot list on TTLG forum, but for some time I really thought there was some secret to open the big vault in the bank and I just missed how.
The reason is that so many loot objects are hidden, often with no real logic behind that. Some of them are even under your feet and you might overlook them. I mean, who really looks at some generic balcony you are supposedly only to climb on to get to some other place?
The difficulty is really a mixed bag. While I didn´t have much issues with the Stefan riddle(the Super Mario jump area was more a nuisance than really challenging - otherwise the cathedral is nicely designed) or with the main quest, other things were not that simple. What really is odd that I don´t see much logic in some aspects. You must not get the bank alarm get off because the story says it then goes on lockdown. While I can see the idea behind that it´s not that the bank seems to be unescapable or the security unbreakable. We will not find out because the alarm will make you fail.
Then we have no "no kill" restriction to my surprise. Some guards are helmet guards and unless you use some of the rare gas items, you either evade or kill them. I guess at some point the author realised that the whole mission is really demanding and so you are at least free to kill enemies to make it not too frustrating.
And while the design of the map is overall really well made and the buildings are nicely detailed, there are some things that feel like really unnecessary restrictions. You have to enter a lot - if not most - buildings by climbing and roping. While this can be fun and I had some with that, I don´t see a reason why the author then added a door in the building which you however can´t open, because it´s not a door, but just a "decoration". I mean, adding a switch to open it from the inside would have been helpful, but there isn´t one.
And because you are very likely to have to backtrack a lot in this mission you must climb into the building again, because you discovered a readable later that told you you need some important item from that specific place. Sigh.
While I like the ambient sound at first, after some hours of playing it really started to annoy me. It´s a rather repetitive sound. Reminds me a bit of a mix from the ambience in some T2X levels in the city and Hitman: Silent Assassin. I would have added some more ambient sounds for different areas outside. While this one in particular is fine if you don´t spend too much time outside, after hearing it for around 5 hours or so you might start to question your life choices...
So I subtract some points from the atmosphere which is otherwise good and some places use custom sounds, too.
Story-wise it´s ok. E.G. meet some old "friends" like Ramirez. Readables are good.
However, I can´t say I really enjoyed the mission. In the beginning and later on for some parts, but there was also a big frustration factor.
I would recommend it, but only if you are really experienced in the game, have a lot of patience and search every room in a very painstaking manner(I really mean this).