The cardboard box trick doesn't actually work in Metal Gear Solid 2, at least not any better than you'd expect it to work in the real world
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.