Hello, just joined. I thought I'd relate some older games that seemingly no one else I knew could beat, but I managed to. The last console I owned was a Genesis and have never been into them since; now I just play PC games.

Atari 2600-Most games for this system had no end and were played for points, but some did:
Raiders of the Lost Ark
Superman
Haunted House
Great game, but I could only win at level 7 or 8, it was too difficult at the really high levels.
Pike's Peak/Ghost Manor

NES
Mike Tyson's Punch Out
I actually found him easier than Super Macho Man. I think the code to go straight to Tyson is 007 373 5963.
Dragon Warrior
Took forever but I did eventually win.
Bionic Commando
Weird game, took a long time to figure it out.
Metroid
Wasn't too difficult, took a while though.
Karnov
Extremely difficult and very annoying-the ending was a just black screen that read "Congraturations-The End", with the misspelling being correct.
Deadly Towers
Buggy game that was very difficult to beat
Kung Fu
Not too tough, the end boss was like fighting a clone of yourself.
Castlevania (original)
Marathon sessions were needed to win this, because the 30 player cheat didn't work for this game.
Double Dragon
Not super tough, but challenging
Contra
Rush'N Attack
Tough, tough game.. took a long time to win. Love the name play on "Russian".
Super Mario 2
Trojan
#1 complained about game
Ghosts 'N Goblins
Lots of trial and error, beat weapon to beat Satan was the cross shield

Genesis
Phantasy Star II
Hard game to beat but I did eventually.
Starflight
One of the best games ever made for the Genesis, this one took a while also but was very fun
Sword of Sodan
Yes, I actually beat this piece of crap.
Sword of Vermilion
Golden Axe
Good port, liked the battle mode more than the actual game. Not tough to win.

That's not all of them but if you have some of your own, please post them.

how about escape from mars starring taz for the sega genesis? that game was impossible

Rigledorn's Last Crusade... hardest game ever.

silver surfer nes
double dragon 3 nes

Ninja Crusaders for NES.

I was unlucky enough to figure out it was possible to turn into an animal form after I beat the game.

"The Simpsons" Bart Vs. The Space Mutants I could never beat that damn thing. I could only make it to the third stage with two lives tops then die.

"The Legend Of Zelda: The Wind Waker" on the Gamecube is VERY hard to beat! I can get really far, but I can't get past the part where you have to find the Triumph Forks before you take on Ganon!