In an odd turn of the tables, First party support for the Nintendo DS is often met with mixed/mediocre reception from fans. Most would say Nintendo's output on the DS wasn't up to the company's usual high standards, containing relatively weak entries in Zelda, Metroid, Yoshi, Fire Emblem and Star Fox series. The general consensus is that 3rd parties regularly outdid Nintendo's own efforts on the DS, at least in terms of critical reception. Nintendo handhelds are no stranger to strong third party support, but it's very rare for a Nintendo console to have better third party support than first party support.
In the case of established franchises, I can see where they were coming from. Super Mario 64 DS was a neat tech demo, but held back by the lack of an analog stick. Not everyone was in love with the touch based Zelda games, and Metroid Prime Hunters was a great shooter, but far from a Metroid game.
However, the Nintendo DS also birthed what I consider to be Nintendo's best new IP output since the NES. DS was where Nintendo started doing things they'd never really done before, haven't done in years, and arguably, haven't done since. Of course we can start with the Touch Generations line, spawning non-game hits like Nintendogs and Brain Age. But there's also weirder stuff like Elite Beat Agents, Big Brain Academy, Electroplankton, Rhythm Heaven, Trace Memory, or Hotel Dusk: Room 215.
That's not even getting into their Japan only games. Like Daigasso! Band Brothers, the Tingle games, Chōsōjū Mecha MG, Jet Impulse, etc. They co-produced two Shonen Jump fighting games. Even some of the established franchises were taken in weird directions. Kirby Canvas Curse was one of the earliest showcases of the DS' touch screen, Wario Ware D.I.Y. put the Microgame creation into the player's hands. Mario Kart DS marked Nintendo's very first foray into the brave new world of online multiplayer, Advance Wars took a darker turn with Days of Ruin, and the aforementioned Metroid Prime Hunters turned Metroid into a DS equivalent of a portable Quake III.
So while not Nintendo's best first party showing, I consider the DS to be Nintendo at it's most interesting and experimental. I'm hoping Nintendo employs a similar and better level of experimentation on the Switch.