Well, its difficult to answer properly... I think that you don't like at all difficult games, and you want to play easier ones (Kirby: Triple Deluxe, for example, its an easy game).. Or you've had a bad period with that New Super Mario Bros.U and then you've left it. Or even, you've been playing two different games at the same time, and you preferred to play the other game instead of NSMB. U... (I remember in early 2014 that I was playing Pokémon SoulSilver and Ratchet & Clank at the same time :)).
Well, and talking about difficulty, I'm a little bit agree with you. The latest Nintendo 3DS game I've played was Super Mario 3D Land, but some levels were very difficult, I died more than 5 times in some levels and I've got bored of 3D Land when I was playing the special worlds. :/
But give it a try, don't give up. I guess that if you put it effort, you'll be able to enjoy the 2D Mario games in Wii U again. You can change that habit if you put effort.







