Biggest disappointement would be Rhythm Heaven Fever. It's kinda very overrated :/

Most disappointing: NSMB2

Least disappointing: Pokemon Black 2.

I still remember being rather pissed at the Black/White 2 announcement.

Least disappointing is a toss up between Xenoblade and Kid Icarus. They both are amazing games that went far beyond my expectations

I havent played a disappointing nintendo game this year though...

Ryan
Although i like KI U, i was expecting tighter controls and a bigger adventure factor, still a good game

About Mario tennis, i dont get people who say it lacks content, ive put 70+ h on it, minigames are great and it has tons of secret clothes and stuff to customize your player, the controls are perfect and the online is endless
the best Mario tennis to date imo

Most disappointing...
Metroid 2...
I heard it was terrible before I downloaded it, and it still managed to disappoint...
This game receives far more love than it receives, and it doesn't even get that much love...
The least disappointing game is definitely Xenoblade...
It may very well be my new favorite game of all time...

I never got to play a lot of Nintendo games this gen so I will have to say the best was Twilight Princess though I didn't get very far. I need to take my father's Wii off his hands.

The most disappointing was New Super Mario Brothers. I thought they did a terrible job bringing back 2D mario. The more I played the less I enjoyed it. The whole game was a tutorial, it was way too easy, I had 99 lives the entire game, and it never felt right or fun. I loved Super Mario 3 and they did not deliver. I beat that game, almost wishing I never played it.

Honestly, my most "disappointing" Nintendo game is Super Mario 3D Land. It's a good game, but I just like the other games I got more.

Kid Icarus being my post played game on the 3DS followed by, I believe, Kingdom Hearts and Ocarina of Time. Of course KH3D isn't a Nintendo game.

I know Super Mario 3D Land released last year, but I got it this year.

I missed the this year part of the title :| but I did play NSMB this year.

I doubt the newer 2d marios have improved in the areas that I would care about?