Self explanatory. And no IWBTG, we all know that's impossible.

Also, this must be it's normal difficulty.

My list:

Devil May Cry 3, original

Fallout 3

The Elder Scrolls 4: Oblivion

Most megaman games at first.

PacMan, no lie.

Every single multiplayer game. I'm too used to stupid/predictable bots.

The Elder Scrolls 3: Morrowind. Couldn't even defeat one enemy. Apparently I have to level up through one of the teachers in the first town before I can do anything.

Gothic III due to a terrible game mechanic that prevented me from killing anything.

Pokemon Emerald, third gym.
I seem to get stalled on every third gym, actually.

Erm...

MegaMan 2
Ultima Underworld II (It's not so much that it's difficult, it's that it requires so much thinking and puzzle solving)
QWOP

Also Guitar Hero 3 if you include DLC. TDWDTG is freaking hard.

All Megaman games.

TOUHOU LABYRINTH
I DARE YOU!
I DOUBLE DARE YOU! >:V

Pacman.

Some sort of tie between The Legend of Zelda: Majora's Mask, Super Metroid, the ORIGINAL Metroid, or Wind Waker.

...Well... Wind Waker isn't so tough as much as the Triforce shard collectathon is tedious.

Castlevania: Order of Ecclesia was tough and took me 8-9 months to beat. I think I got lazy and stopped playing for a while before finishing it.

The hardest multiplayer game I have played is Descent 3. The game's controls are complex and most of the players have been playing it since 1999, so if you're a newbie, you're gonna get whipped big time.

I`ve never really had any trouble with games until I bought Final Fantasy XIII. It was my first Final Fantasy game, and at first, it was relatively easy, but it has a huge difficulty spike later in the game, and one of the bosses took me (an almost continuous) 3 days to beat, and a week the second time. I haven`t beaten the game yet, either, even though I got it in March, but that`s just probably due to lack of time.

I'd say the original Final Fantasy just because they don't exactly specify where your supposed to go. It took me 2 months to figure out where to go after you get the 3rd crystal and thats because i finally decided to cheat and use a walkthrough XP

Pokémon Red & FireRed; I always get stuck on the 2nd gym, even when I have a super-effective type.
Starfox 64; I always get stuck on Sector X.
Need for Speed Hot Pursuit 2 (PC) online; Everyone always cheats by modifying their car files.
That's all I can think of for now.

Ninja Gaiden Sigma for the PS3.

Pokémon Ranger (1) that darn Charizard, it took me over 100 tries. Then I beat it easy, same with second time. Then I got stuck at the last Go Rock (S)quad base. It took me a year. Now I consider myself to be a master Ranger in 1 and 2 (VONTAGE STYLER FTW!!!).

I have played some hard games but the hardest ones i've played , are the ones im playing now.

Fallout 3

and Devil May Cry 3 ( Original, not special edition)

Fallout 3 and Super Mario Galaxy 1 & 2 (Beat them Both)

I say Sin & Punishment: Star Successor, if you really want to be punished in a shooter then this is it. I can tell you my arms and hands got tired after beating it on normal....Also, good luck with the final stage, YOU'LL BE NEEDING IT. :/

Pokemon Ranger

I could never capture that steelix o.e

I thought Pokemon ranger was pretty easy... huh... I must be a natural at drawing circles

Well, hardest game, uh.... well, I could never beat Yellow version.

Donkey Kong Country 2. The final boss was too hard to beat. His attacks are difficult to dodge and I couldn't even get close to the halfway point in toxic tower level.

The hardest game in the world, under the right conditions is the Thief series. You are a master thief, not a killing machine.

I can't seem to finish missions like The Lost City and Return to the Cathedral. Once you run out of equipment, these levels become fiendishly hard. I remember watching my dad play the Lost City. He kept getting killed while trying to cross the lava. He ran out of healing potions at one point, and for most of the mission, he has almost dead.

Resources and equipment are about as hard to find as items on Resident Evil: Code Veronica.

Now if you're a brilliant Thief player, you don't even need one healing potion.

Also, I can't seem to get past some of the fan-made missions (Ranstall Keep ).

the hardest game I played is pacman I guess my reflexes aren't good enough to watch the ghosts and turn at the same time.

Pac-Man isn't so hard for me, but the Megaman series is just so hard when you intially fight every boss.
Trident remembers when I first started Mega Man 3 and the sheer torture it was...

Gutar Hero, or any game featuring an instrument, is just too hard for me.

Aside from that, Mario Kart Wii is the hardest if you mention the fact almost everyone on Worldwide races use the infamous Funky Kong + Flame Runner combo.

Final Fantasy IV because of the Element Lords and Mother/Earthbound Zero but it was illegal to play in english