For Looking Glass, more like Crowning Level. Just mention the Thief II level Life of the Party to any Thief fan and they'll grin and remember the first time they played that huge, very open ended and incredibly well designed mission that combines burglary via rooftops of noble mansions, banks, a necromancer's spire, and dingy tenements with Garrett's gatecrashing of that party. And Karras knew you were coming ALL ALONG! Let's not forgot what happens after you read the Karras' New Scripture... arguably the biggest scare of the entire series, though you weren't in any danger!
The way Garrett defeats the Big Bad in all three games: He uses nothing more than his expert knowledge of stealth and subterfuge.
Thief : The Dark Project : The opening credits and the tender but weary score during the final cutscene... which then transforms into a Trent Reznor-style piece...
Just about the entire Thief II : The Metal Age soundtrack. In particular Shipping and Receiving, which creates such a haunting atmosphere of grey and soulless industry, Eavesdropping, which conveys the surrealness and spooky secrets of the Mechanist seminar, and Trail of Blood, perhaps one of the most haunting tracks ever.
Intro and outro music in the style of Nine Inch Nails is present in all three games, possibly to add contrast to an otherwise purely ambient and mostly silent soundtrack.
The soundtrack ofThief : Deadly Shadows also gave us top-notch ambient music, with lots of distinct leitmotifs. Some of them would nicely fit the definition of Crowning Moment Of Moody and even Crowning Moment Of Scary - if tropes like that existed...