Which are the games that are challenging and which are the hardest

Hello!

The difference between the two would be that a challenging game puts you through obstacles that require you some skills to beat it (not exactly the exact opposite of facerolling a game but close) and you CAN beat it. And for "the hardest" I mean games that are almost impossible to beat/take very much skill/time(or more likely devotion) to beat. Oh,and these are pretty much unrelated to difficulty levels,as most games are challenging and hard on high difficulty levels, at this post try to concentrate on games that are challenging or hard by default.

I'd give examples too:

challenging : Far Cry, Driver: Parallel Lines(shaking off the cops)

hardest : El Matador, Driv3r (some driving missions)

Killzone 2 on veteran is a pain in the azz to beat.

Challenging:

-Mass Effect 1 & 2 (On Insanity)

-Armored Core: Four Answer ("S" ranks on all missions)

-Vanquish (Completing all challenge modes)

-Gears of War 1 & 3 (Insane Difficulty)

Hardest:

-Ninja Gaiden II (NES) *witnessed its chaotic levels*

-Lost Planet: Extreme Conditions (Extreme Difficulty) *Probably the Hardest :P

-Megaman Zer0

Completeing Demon's Souls was the hardest to beat

I need to make a thing clear. By this phrase "at this post try to concentrate on games that are challenging or hard by default." I wanted to say try to concentrate on games that are challenging or hard EVEN ON EASY difficulty, the game being made to make you sweat. The list may be shorter this way, but more interesting to know such games.

This is because I saw posts that said some games are hard on the insane/veteran (and other) hard difficulty levels.

Dark/Demon Souls. Final Fantasy.