Again, it has nothing to so with yearly releases.
The only thing preventing them from releasing faster is Nintendo's size. If Nintendo was a bigger company, you can safely bet most of these games would come out each and every year.
Ok, so let's do it based on Gameplay shall we, to prove it's not just "roster updates"
New Super Mario Bros U (Everywhere) - I'll give you this one, since not much has changed, but it is the pinnacle of 2D Mario games. The level design is second to none
NintendoLand (Everywhere) - Various ideas never included in any game before
Game & Wario (Everywhere) - Various ideas never included in any game before
Sing Party (America and Europe) - Karaoke...not really much to add to this
Lego City: Undercover (America and Europe) - A massive openworld made of Lego that you can build up and destroy. Uses GamePad in exclusive ways
Pokémon Rumble U (Japan) - Dozens of new mechanics plus the first Wii U game to use NFC
Pikmin 3: Implements new features such as controlling three characters at the same time.
Wonderful 101: Massive new IP with loads of features that are not possible on another console
The Legend of Zelda: Wind Waker HD - It's a remake, yet it adds loads of cool features including an online message system
Wii Party U: New mini-games using various ideas never included in any game before
Donkey Kong Country: Tropical Freeze: not too familiar with many of the mechanics here, but it's not that "roster update"-ish
Mario & Sonic at the Olympic Winter Games: New mini-games based on the winter Olympics, plays different.
Super Mario 3D World: Four player co-op. Various new power-ups that change how you play a 3D Mario...unless you could climb up the side of walls before.
Wii Fit U: Offers various new exercises and comes with a pedometer that helps you track stuff more easily
Sonic Lost World (published by Nintendo in Europe): Features completely unique level design unseen in any Sonic game before
So, how are these just "incremental" updates?