Very difficult on expert if played ironman, took me 5+ tries blackjacking every guard inside. Ghosting this ironman on first try would be unreasonable.
The mansion itself is small and tight where you are constantly "pushed" into uncleared rooms with no ability or time to figure out what you're heading into due to constant guard pressure in crampy lit interiors. I didn't mind the challenge, but it's annoying to have zero ability to recover from detection with no flash bombs.
The ending is ruined by a very strict loot requirement and a key/frob pixel hunt wearing out its welcome, causing me to drop the fm instead of consulting a walkthrough.
But hey, at least it's visually impressive, sometimes I just had to stop and admire it.