Nintendo's problem is that they're living off nostalgia and soccer moms, and the soccer moms already have Wii Fit for the original Wii, and there's no sense upgrading since it still works. Put in the yearly Mario rehash (how many "New" Super Mario Bros. can there be until it's not "New"? I think they've already hit that point) and the bi-yearly Pokemon releases and you have a chunk of their sales.
Third party companies are stationed elsewhere. And I'm not just talking about overblown franchises like Call of Duty or the annual sports games. Everything from tactical games to JRPGs and everything else have found quite a nice spot with the other consoles, and their lack of senseless gimmicks.
If Nintendo doesn't make some new first party titles soon, and they don't blast off, I'd say they're looking pretty bad. But, to establish new first party titles, you have to have your console in a
lot of homes, being played by dedicated gamers instead of the "family console" that sees a few Mario games and maybe a Zelda title, Wii fit, etc.
Without the success of Animal Crossing and Pokemon, the 3DS wouldn't be doing as swell either.
Add in the fact that casual gamers are increasingly going to mobile to get their quick and cheap gaming fix, and it's not looking good at all.
I'm not saying they're going to crash immediately - it may be more akin to a train slowly running out of steam - but you can only add so many Pokemon until people get tired of it.
Innovate or fail, that's how it's always been. If you don't do better, someone else will.