This isn't too hard. I just want you to rack your brains and think of two of the hardest moments in gaming which you've come across, but also the most enjoyable. Since I'm so generous I'll start off with two even:

WARNING! POSSIBLE SPOILER ALERT!  (There's nothing too great, but avert your gaze if you want to keep them a secret )

1. WELCOME TO HELL! (Cave Story)

Picture the scene. You've just defeated the final boss of Cave Story. Not only that, but you also skipped out the Booster v 0.8, and got the 2.0 version much later in the game. Not ONLY that, but you also got the Tow Rope, and rescued Curly, drained Curly, and restored her memory. You go back into a house to save before the ending, and the door locks behind you. You enter a hole in the floor, go see the sign (which says "WELCOME TO HELL!" , continue forwards, and die.

And then you die again.

And again

And again...

That's hell in Cave Story; a series of insta-death traps, followed by an onslaught of enemiesmixed with a crumbling path, then both together, with a boss at the end, then ANOTHER boss at the end, with 4 different forms, the hardest in the game. All that with no chance of saving, returning, and the only way to get more health is if you're lucky enough for an enemy to drop one...

Why do it? Well, there's a timer, so you feel as though you're obligded to beat a set time, the ending is worth it all, there's story dialogue all the way through (what REALLY happened here?) and the music is amazing. 

And, well, you did all of that at the start, remember? Why not get your reward?

Current score- 170ish deaths. 1 success

2. Grandmaster, The Perfect run (Super Mario Galaxy 2)

There you are. You've just completed what some say is the best game of all time. You've got all 120 stars in the main game, ythen you got the free-roaming, explorer's 120 stars as well. All is well and done. You go to bed, when...

*GRANDMASTER GALAXY IS NOW UNLOCKED!*

Out of curiosity, you visit the galaxy. What do you find?

Well, you find the following, in the following order:

• A minefield, which can only be negociated with Yoshi
• A panel of switches with lasers firing at you
• An electric fencing with no platforms, just clouds and a windmill
• A series of disappearing platforms and laser enemies
• A pull-star world with cannons and fencing
• A series of floating platforms with Hammer Bros, and 3 Boomerand Bros who have to be killed at the end.

Vanquish, Challenge Mode, Challenge 6.

Each Challenge comes in five waves.

Wave 1: About a dozen mooks and a melee boss. Not so bad if you don't freak out at fighting the CRYSTAL VIPER.

Wave 2: Dozen mooks, dozen helibots (thehse bastards are murder unless you kill them in the air), and an early game boss. Uh, shit. This particular boss is hard. Oh well! Not too insane, really.

Wave 3: Half dozen mooks, two drill giants, one flamethrower giant, one standard giant, and one missile giant. Shit! If you don't know what you're doing, this fight will annihilate you. Luckily you have the blade shooter right near your spawn point, and careful grenade timing gets rid of the mooks right off the bat...

Wave 4: Eight or ten gliding blue mooks with shotguns (shit) and two flying gatling platforms (SHIT). Oh, wait, that's not all, you also have to fight two of the boss-fight level cat transformer robots who have as much health as any boss. SHIIIIIIIIIIIIT! Ironically this is one of the easier waves if you know how to dashh-cancel, but the sheer fear factor of this fight can't be underestimated, and if you don't kill those gatling platforms then you are going to die horribly.

Wave 5: One dozen rolly robots.

Wait, what!?

They never make you fight more than three of these things in the campaign! They're extremely durable when moving, murderously powerful when standing still, and can move around in ways that no other enemy in the game can! Who's diea of a joke was this?

Oh right, and you also fight THE FINAL BOSS FIGHT, against two bosses, only they're faster, use their attacks more often, do more damage, and hate you more. When you kill one of them, the other goes absolutely bugshit, speed being cranked up to an extreme so high that the only way to hit them without AR mode is the lock-on laser. In the campaign you're given a boost to match, but in this fight? You're on your own, bitch.

All five waves must be completed in succession. No checkpoints. You die, you start over from the beginning.

THe final wave alone is a fifteen-minute gauntlet of dodging and shooting and fleeing and screaming.

Beating it was the most satisfying thing I've ever done in a game.

Deaths: about 35

Wins: 1

The most recent one would be getting Gold on the Top Gear van race challenge in GT5. AFter several tries and profanity, I finally got first place by 0.002 seconds.

Are you talking about the one to unlock the track? Because that barely took me any time at all, once you learn how hard you can bounce off the opposition without being penalised

I would say Mirror's Edge time trials, especially the DLC levels

If it's the challenge with the big old vans that unlocks the track, then yes. I don't like using the bumping method for races, it cheapens the win for me.

Metroid Prime - Phazon Mines, the first segment

The most difficult part, and the most rewarding.

Vanquish - Tactical Challenge 6. it dosent matter how satisfied i was after completing it, it dosent compensate for the amount of times i failed.

but my victory against the final wave was awesome. and i almost died a few times, making it that much sweeter when i completed it that time.

Bayonetta - Alfheim Portals. played it ages ago so cant pinpoint which one was the most difficult, but some of these were very hard. satisfying to finish!

FF9 - Getting Excalabur II, which involved racing through the game in 12 hours on the PAL version of the game where the clock actully ran faster than the US or Japanese versions of the game. not satisfying enough though, not enough reward for actully getting it.

Ouch, that sounds...awesome.

Seriously, I need to do that now

And I remember the Metroid Prime on (wasn't too difficult sadly!) and some of the enemies in GT5 are awesome

F1 2009 (wii) without any driving aids, winning a 100% race wth hard CPU, damage, tyre ware etc. was also very tricky yet satisfying...

Aladdin for the SNES the Lava stage where you have to carpet ride through a really narrow passage way with lava chasing you.  It's a classic 2d gaming moment with sinmple up, down, right, and left controls that is just intense in a hardcore way.  Perfect example of how gaming can be mad simple and yet mad hard.  Very old school Mega Man-ish in that way.

The Original Mortal Kombat for SNES where you have to chop blocks of wood and metal by button mashing on A B at the same time.  Freakin insane especially if you are with a friend taking turns.

I can't think of to many modern examples because gaming has just gotten mad easy.  I'll give a shout out to Smash Bros. Melee Event match 51 with Giga Bowser and Company.

Never played to other two...but I can vouch for the last one