For me there's some contenders.

2005: Mario Kart DS + Animal Crossing Wild World + Super Mario Strikers
2008: Mario Kart Wii + Smash Bros Brawl
2017: Mario Kart 8D + Mario Odyssey + BOTW + Mario Rabbids.

2008 or Fiscal 2009 is the year Nintendo decisively dominated, not just videogaming, but home electronics as a whole.

Over 400 million pieces of software sold.
Over 57 million hardware units sold.

On a personal level, it´s still the 1991-1992 period with the SNES, so many gems.

2008 and 2009 were incredible years for sales, but for me they were kinda average in terms of their game lineup.

In terms of good games, for Wii's 2008 I'd nominate Mario Kart Wii, COD World at War, de Blob, No More Heroes, Shaun White Snowboarding, World of Goo.

For 2009, Silent Hill Shattered Memories, Wii Sports Resort, NSMBWii, COD Modern Warfare, Dead Space Extraction, Muramasa.

I don't think either are as bad as they're often made out, but at the same time I don't think they're anything really special.