Wii.
It did absolutely nothing for Nintendo's long term prospects, and indeed probably caused Nintendo and fans to have an overly inflated opinion of itself and its future. It alienated 3rd parties in that because of its lack of power the big HD multiplats on PS360 could not be put onto Wii and look at all decent, they were poor imitations of the real thing. It also caused a pretty much permanent rift in the console gaming fanbase becuase of the inferiority of 3rd party multiplats.
Nintendo went after a market that had no long term prospects in consoles, when it should have tried to carve out a larger fanbase with the core gamers. Now that so many core gamers have completely turned their backs on Nintendo they have an absolute crisis on their hands in home consoles. Under Wii's influence Nintendo has lost money for the first time ever(?) or at least in a very long time.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix
