But the AI in stealth games is literally trained to go out of its way to not detect you.
The only strategy that somewhat worked for me was perfect accuracy tranquilizer shots, to knock them out instantly. That's probably the hardest game mode I've ever played.
Halo 2 on Legendary difficulty was ludicrously hard too
On the other hand, I loved MGS3 on euro extreme! It really required mastering every trick in the game. Every little advantage you could squeeze into a boss fight was essential. Escape from Groznygrad was hell, though. By far the single hardest part of the game.