Difficulty: ⭐⭐⭐⭐⭐⭐⭐⭐ Controls are not always intuitive and actions are mapped to uncommon buttons. Lots of what I call "Kojimbo BS"; chief example, confining you to a small enclosed space and spawning invisible tanky enemies, ensuring you lose rations (healing item) and ammo.
1
Metal Gear Solid 2: Sons of Liberty
Difficulty: ⭐⭐⭐⭐⭐⭐⭐ Less "Kojimbo BS" but still there. More options for combat. Easier bosses; except Solidus, imo he has too much unpredictability (still fun though).
2
Metal Gear Solid 3: Subsistence
Difficulty: ⭐⭐⭐⭐⭐⭐ Hardly any "Kojimbo BS". Easiest bosses out of the original trilogy. Subsistence version adds 3rd Person camera which makes stealth much easier than usual fixed camera.