This thing had be laughing out loud several times - and *this* broke me completely:
Instant-Failure Stealth Levels. Ack. This brings back horrible memories of a Goldeneye level where if you tripped an alarm, an infinite number of bad guys poured forth. We knew a man who failed that level 37 times, then got the Infinite Health cheat for it and came back. He intentionally tripped the alarm, the guards rushed out. Laughing maniacally, he proceeded to shoot those fuckers for four hours, killing 1,183 of them - 682 with groin shots - before his thumbs cramped up. Your game should not create this kind of bitterness.