Most of this negative hype is probably from PS2 or Xbox fanboys, who are probably just jealous that we actually have good games on our systems. You could count the actually good games on those systems with one hand. To count all of the good games on the Cube would take... uh, several hands.
But seriously, I think a huge problem these days are the "casual" gamers creeping influence on game design. They just want to jump right into a game and "kill stuff". Case in point, two kiosks in my store. One Xbox with Halo and Cube with Zelda. Kid walks up to Zelda, spends two seconds trying to move Link through a door, too stupid to realize he has to push the big green button to open it, says "This is stupid!", walks over to the Halo demo and starts shouting out "Cool! Blue blood!"* I remember when one got a game, he or she actually sat down and read the instruction book before (or during) playing so he knew how to play it. Nowadays, people just want to know how to jump in a car and run over hookers.
Uh, what was the question before I started ranting like a moron? Oh, yeah. The Cube isn't going anywhere. I have some friends who own Xboxes and they often give props to the Cube (in fact, one considers Mario Sunshine to be the greatest platformer ever and he even has the Zelda pre-order disc even though he doesn't own a Gamecube... yet). Nintendo's still making a profit, and I hope they don't drop the price to $99, because a console the same price as a handheld looks pretty bad.
Nintendo will be around to the next generation and the one after that. After that one, I'm not sure. What do you think I am, some kinda psychic?
*(Apologies to Halo fans, it is actually a pretty good game. Please don't use that Needler on me.)