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.
Crosses the Line Twice: In mission 6, elevator doors can keep opening and closing on a victim's head. And if you go back to that area later, it'll still be the case, because there is apparently no way to actually get him out.
It's an idle enviromental animation. But still... the poor devil...
Also, the The Expansion Pack is a variation of this trope, since it heavily improved the already great original game further.
That One Level: Du Plessis Diamonds, for how cramped it is, you WILL get shot. Also, the Taronne residence, where lethal weapons will blow up the carelessly scattered explosive hazards and kill anyone in the blast.
Mt. Threshold is pretty tough as well, it's the largest level in the game, so it can be difficult to keep track of where you've been, and there's about a dozen places where you can get ambushed easily.
The solution? Teargas. Lots and lots of teargas.
The Old Granite Hotel. Not only are there a lot of highly skilled opponents with hostages, you're also on a 10 minute time limit to defuse several bombs. Spoony's playthrough of the level was titled "I die a lot," took several days to film, took over fifty lives, and had to be compressed into a montage.