It's not the difficulty that bothers me. As mentioned above, for Metroid it's the controls, for Zelda it's that it on rails (I HATE on rails with a passion) and Donkey Kong I just simply find crap and boring, regardless of how challenging it is... I'd rather play Cut The Rope on my iPhone, it's much more fun. The same applies to things like Balloon Trip, Capt Falcons Twister Race, Octopus Dance, Tak's Ninja thing and Yoshi's Fruit Cart. Out of which I prefer Yoshi's Fruit Cart funnily enough.
The only one I'm yet to try is Pikmin Adventure, I can imagine that being my favourite of the lot but I do wish the game was online so I could actually enjoy it!