I just beat it for the first time last year. Though I hadn't put any real effort into beating it as an adult until then, as a kid, I couldn't beat it, but my older sister and father could.
For me, it's Ninja Gaiden 2 and 3. Ninja Gaiden 1 I can fly through the whole game effortlessly until the last boss, which I can beat, but it isn't easy. And it's not even a game I am that familiar with, its just really easy for me for some reason, but part 2 and 3, I get frustrated and stop playing after the first couple stages.