The title is self explanatory. Just post the hardest game you have ever played,
or at least one of the hardest. Post as many as you like.

Here are a few:

I have tried Assassin's Creed Brotherhood lately, and it was really hard to manage.

Final Fight
the Enemies are easy to beat but the damage they took...
Man Its hard.

I can't get past the Dark Oracle in Assassin's Creed: Bloodlines.
No matter how many times I try, she always ends up killing me.

Other than that, I haven't had a lot of trouble with video games. Mainly because I am too much of a wuss to venture beyond the "Easy" difficulty.
Even "Normal" is too hardcore for me. ;>

Asphalt 3D, because one of the races in the championship mode is impossible for me to beat. :x

Pokemon Firered and Leafgreen! I can't beat Gary Oak, no matter how hard I try XD.

In fact the only reason I play it is just because Pokemon games these days are too easy. Beat Pokemon white in two days. Never was able to beat Firered/Leafgreen, even today.

Madden (the football game) on All-Madden difficulty. I get killed every time.

Devil May Cry 3 ON DANTE MUST DIE MODE! Yes, all the modes are incredibly difficult. (almost finished with very hard mode) But, I thought Hard and Very Hard mode were hard enough. But, Dante Must Die mode is impossible. You litterally have to do everything in the game. (get all Blue Orbs, possibly have three gold orbs, get all abilites, etc.) I'm not willing to dedicate that much time just for one game.......

Streets of Rage 2 on Mania Mode with only 1 life, starting from stage 1.

Good luck.

Magicka's a pretty damn hard game... Especially single-player, I haven't even finished the game in co-op, I have no idea at all how you're supposed to do it in single player. Dem Yetis .-.

Touhou series.

Yep. Didn't make it past the first stage.
Fun as all hell though.

Just a quick heads up that you're straying from the point of the topic. If you wanna talk about Streets of Rage 2 make a topic about it.

Aw, crap. Seems like people do that sometimes.

The Impossible Quiz, on the internet.

I just recently found out how difficult No More Heroes is on Bitter mode.

Cave Story on Hard Mode. (aka the mode where you hope to survive as a hamster againist Saxton Hale and Chuck Norris without getting hit)

Have fun!

fallout 3 hard mode
weapons are more powerfull
never finished on hard mode

Super Meat Boy.
'Nuff said.

Mega Man X5 on Xtreme mode would be harder if continues on game overs didn't send you back to the same spot that losing a life does.

Also, Mother 3 without getting a game over. OH THE PRESSURE!!

Pacman.

I'm not even kidding. Getting past levels 6+ is voltorbs-to-the-wall hard for me. Final Fantasy XIII is also difficult if you don't take time to level up.

I would say Halo: Reach. For fun a friend and I tried a Firefight match with what would be the hardest settings (including making the default weapons golf clubs). We were dying all over the place.