They need to innovate, plain and simple.
Asking core gamers like those on this board is kind of pointless, because the main responses you're going to get basically boil down to "make a Playstation". Which would be fine, if there wasn't already a Playstation (and XBox on top of that) filling that market need already.
NX needs to be something different, new, and fresh in an immediately understood and appealing way. Easier said than done, but that's basically where Nintendo is at.
"I need", "I want" coming from gamers who are 25-40 years old isn't really the market Nintendo should be listening to either (hate to say it). They need to get a new generation of kids otherwise they will not have a foundation for their business for the next 10-20 years. They need to take more chances on new IP like Splatoon, but the IP must be marketable.
A Nintendo that's basically stuck selling to 40-year-old men who are trying to relive their youth is a bit of a sad prospect, they need a new generation of fans. In the same way you could say that The Little Mermaid, Aladdin, Beauty & The Beast, and The Lion King brought Disney a new generation of fans.
