In Mission 12 the bystanders do not react to anything that is happening.
The Mission 7 briefing text misspells 'UN' as 'UF'.
In Hong Kong, the building's are sometimes incorrectly scaled, with the height between windows not being enough to believably occupied.
In Mission 7, metal detectors do not go off when Agent 47 is dressed as a policeman even if he is carrying a metal object.
In the HD Trilogy versions, when 47 jumps across a balcony the sound effect of him grunting is used earlier than when 47 is actually mid jump.
In Mission 4, bedsheets are left out in the rain.
The butler in Beldingford Manor uses David Bateson's voice when Alistair requests more whiskey, but his voice is different when he actually speaks again.