Invisible Inc.
Dunno what else to say other than it's a good game, especially as the game progresses and scenes slowly degrade from a state of order to a state of disorder.
See, everything in the game runs on a pattern, and your objective is to get through those patterns as best you can without disrupting them. Now, the thing is - if you do wind up disrupting the pattern - say, through causing a guard to be distracted/notice a noise made, getting recorded on a security cam or - possibly the worst of all - getting spotted - the pattern begins to crack.
You take down a guard to keep them from shooting an agent, they'll fall unconscious but will eventually get back up - you either have to spend an agent to keep them pinned, or you have to leave before the guard wakes up and begins to hunt for your team. Something similar happens even if a guard gets merely distracted - they will never stop hunting you.
If you do kill a guard, and - barring special circumstances - their heart monitor will advance the alarm meter, which slowly makes the level a less safe place for agents to be in.
You get spotted by a guard and another guard's nearby - it's likely a second or even third guard will notice.
Security cameras will alert nearby guards that an agent is at their position, causing them to go looking... and they'll never stop hunting, similar to guards who have been knocked out.
It's kind of what I imagine Dwarf Fortress to be like - starting off relatively small and either growing into something extremely powerful, or descending into a hectic scenario where bodies lie everywhere and merely breathing wrong can get you shot.
Or both.