You clearly must have been playing on easy. Even on normal, guards DO notice when their friends have gone missing and will actually start searching for their bodies. Trust me, taking out the High Overseer on a 'no-kills/no alarms' playthrough is a pain in the arse. The chair where you have to place Campbell and brand him is patrolled by two guards on slightly different routes. Both have to be taken out within 30 seconds of one another or they'll notice their missing friend, start searching and then find the knocked-out Campbell in the torture chamber. What makes it even more difficult is that there is a third guard who will note the disappearance of the other two after a few minutes. Much re-loading was required to get this section right.Kellogs Fried Chickn said:Although well executed I would not call this a mechanically impressive game. They could have added much depth with the current mechanics had they expanded them a bit.
AI still shoots the game in the foot - no, it'll never be good enough. The guards should start noticing when half of them are absent, sleeping in a dumpster. The game fails in stealth runs as you can take as much time with them as you like, knocking them out and dragging them to a nearby dumpster, often noticing there are less bodies than there should be, creepy.
Also, on hard and above, the guard's perceptions increase enormously.