For me that would be the original Rayman for the PS1.
I loved this game in my childhood, and in a way I still kinda do. But I never really got far in the game as a kid, and now I know why.
THIS GAME IS FUCKING HARD AS NAILS.
Seriously, this game is unforgiving at best. It starts out fairly easy, not too bad. But then the difficulty spikes at Band Land, and suddenly I was getting my ass killed over and over due to ridiculously pinpoint precise platforming, insta-kill spikes, and those bullshit fly enemies that dodge every single attack you throw at them.
You have a limited amount of lives in the game, which you're really really really going to need. And once you run out, you decide whether to go back to the main menu, load up your last save and start the level you screwed up on all over again, or continue and start off at the section of the level you last died on. You have limited continues however and as far as I know, there isn't any way to get more of them besides cheats.
As I said previously, you NEED all the lives you can get in the game, but you don't want to waste all of them and your continues on the early levels, so in a way, you're kinda forced to go back to the main menu to start the whole level again just so you don't use up a continue.
This wouldn't be so bad if the game didn't force you to find every single last fucking electoon in the game in order to have access to the final level in the game. I want to be a completionist in some games because I want to be, not because I have to.
Speaking of the electoons, a lot of them are placed in locations you can't reach until you learn a specific move from Betilla the Fairy. So you have to go back to certain levels later on in order to complete them. And if the little rant about Band Land wasn't enough to convince you how much I hate that place, then the fact that I don't want to have to experience it again just to complete it should.
Some of the electoons don't even appear until you walk or jump in a certain way or position. So you're going to have to look up a guide in order to figure out what the hell you're supposed to do to make them appear.
It was right about after one of the Blue Mountains levels that I couldn't take it anymore. It was far too agonizing for me to continue on. (That and Mass Effect 3 was almost released at the time I was playing, so I got permanently sidetracked from it)
And yet, after all that bullshit, I still can't help but like the game. I love it's art style and it's soundtrack. And in a way they both make me want to play more. But every time that happens I am reminded of the game's cruel and unfair difficulty. So I can't bring myself to play it. Kinda makes me sad in a way.