Okay, who here knows VVVVVVV? Thanks to the Humble Indie Bundle-athon, I'd say a good number. But do you know about Hexagon? Probably not unless you follow Terry Cavanagh on Twitter/have looked at his website. Fact is, I really found the former game to be sadistic to the extent of barely feeling worth it (this is coming from someone who loves Super Meat Boy). Hexagon however, seems to not fall into the category of "so brutal that you can't see the point anymore". In fact I'd say it has a far better learning curve -- by the time I was to level 3, I could easily evade obstacles that once would have smashed me apart without trying. That's not what's special about Hexagon.
It's how it in of itself is probably one of the best motivators for "just keep trying". It does this by something I like to call the Climax Effect. At first you start trying and you're just learning how to play, but soon you start noticing the music and tone and pace and realize -- this is what a final boss fight feels like. This is what some of the best gameplay driven moments in gaming history feels like. Every instant you're still standing makes you feel like a badass or a defiant hero who won't give in to his opposition no matter how large. It's the kind of epic feeling games like Uncharted 2 wish they could create more genuinely. Over my time with Hexagon, I had as much investment in it as I did over the Mass Effect series. Like lightning in a bottle you can drink, Hexagon just does this without so much as blinking.
And the amazing truth is, it shouldn't be able to do this if you take out just one feature. Like, say for one, they added a life system or something that only partially rewound your game ala PoP/Braid -- that would totally break the intensity or make it so intense it'd be too frustrating. And probably the worst thing you could do design wise is making it go form having an intense, alternating soundtrack, to leaving it only with just one track that keeps going on and on -- or maybe not even including a soundtrack. If there was no music, we'd lose our initial prompt, and it would take an actual massive winning streak to get the same kind of effect.
So what I am basically saying here is, go play it. This is the kind of thing so many developers don't understand -- that it doesn't take AAA money and hours put into a game to make this kind of emotion. All it requires is great designing and production of the final product.
Here, you don't even have to look it up: Kongregate.com