I haven't been paying much attention to what the general consensus of the Wii U is, but it seems there are as many Wii haters nowadays as there are Wii lovers (maybe more of the former?).
I have a hard time believing Nintendo will ever (or at least for a very long time) be dethroned in the handheld market. However, I also find it difficult to believe they'll have much staying power in the console market.
The Wii U doesn't look terribly impressive and the major thing Nintendo has going for it[self] is its name. Everybody knows Nintendo. Even though Wii was (I think) the most profitable system ever, I feel like Nintendo focused so much on capitalizing on a new market that they lost sight of their core fan base somewhere along the way. That's not to say Nintendo has neglected them entirely, but their priority seems to have shifted, at least temporarily.
Nintendo has become somewhat synonymous with "gimmick" far too often as of late. Innovation is great and all, but when innovation becomes a fad, things start to look bleak.
What will happen to Nintendo with the release of Wii U? Are they headed out the door? It's hard to imagine Nintendo going the way of Sega, but it was hard to imagine that happening to Sega at the time too.
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"Filthy lawbreaker, unhand that vending machine!" - Casey Jones