These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
From Thief 2: The Metal Age, Karras is the high priest of a splinter faction of Hammerites that worship a deity known as the Master Builder, but in Karras's case, he split from the original Hammerites due to his extremism that takes the form of wishing for the destruction of all organic life. Karras rebuilds his religion around his own twisted ego and desires and freudian slips reveal he places himself above his own God. Karras is responsible for kidnapping countless homeless people in the city and turning them into twisted mechanoid abominations, and our intro to him is his using his special rust gas to painfully kill two innocent people as nothing more than a demonstration for a corrupt sheriff. Karras's ultimate plan is to use the rust gas to wipe out all organic life in the city and to that end, attempts genocide on the woodland peoples, with only Anti-Hero Garret to stop him at the end.
The Hag, Gamall, from Thief: Deadly Shadows, is a legendary serial killer and murderer of children. Gamall has been killing for centuries, ripping the skin off her victims and wearing them as her own to maintain her immortality. This also allows her to take the forms of her victims. A former member of the Keepers, Gamall desires to destroy the organization as well as to learn all of its secrets on glyph magic. In order to re-infiltrate the Keepers and gain their knowledge, Gamall murders a little girl named Lauryl to take her appearance. Once inside, she studies under Interpreter Caduca, eventually murdering the woman so she could be promoted to her teacherís position. When Gamallís glamour fails in front of the Keepers, she slaughters several of them in a rage, despite most of them fleeing from her. She later kills and steals the skin of Garretís long-time friend Artemus and then strangles First Keeper Orland to death after the latter tries to redeem himself. Unlike the previous Big Bads of the series, who were a Well-Intentioned Extremist and Knight Templar, Gamall acts purely out of self-interest, to make herself invulnerable.
That's not unconsciousness; she breaks her neck, but since she can't die she just lies there blinking and occasionally going invisible but otherwise immobilized.
Even better, do this at the docks and you can make her fall into the ocean.
Hell Is That Noise: In The Maw, the chattering, lip smacking, mewling and whining by the... creatures in the level. Completely alien, and extremely unsettling.
Most of the scary environments in the series, really. The bizarre ambiance of the Cradle makes the Maw feel downright comfortable.
The golems in the third game, especially when they find you. CRUSH AND KILL AND CRUSH AND KILL AND SMASH AND KILL AND SMASH...!!!
Fan missions, mods and other fan works :
Fan Wank : Since the storylines of many fan missions often extrapolate from established Thief canon, you're bound to bump into something based on WMG by the series' fans.
It's Short, so It Sucks : The number one complaint about any fan-mission is "I wish it were longer!" Not to say that FMs are bad or short (many of them rival the original missions in length and complexity), but since most FMs are single-level, the fun can only last so long.
They Changed It, Now It Sucks: Completely averted; almost any change to the status quo is seen as a brilliant innovation, especially when pulled off right.