What Keane and Shroobie said, I agree with wholeheartedly, I doubt I'd spend around ten years trying to complete Rayman 1 if it were badly designed or half-arsed.
But, I persevered, I played that game over and over, and yet for all my failings in the game, I could still admire it, it still was fun, at the end of the day, and provided me a great gaming experience, one of which was probably one of the reasons why I like gaming to this day.
However, there will be some games, which either out of bad design or shoddy effort, will be terrible and of course, frustrating, the difference being is that the frustration is on the shoddiness of the game, when I screwed up in Rayman 1, I was frustrated at myself, since only I could be blamed for screwing up, however, in a badly designed game, it could be that I screw up due to how the game functioned, and that ruins the experience, and when one beats an unfair segment like that, you don't get the same sense of achievement you'd get if you beat a properly made segment.