I haven't used one, so I can't comment on how good it is, but I think the Gamepad is indicative of Nintendo misjudging the market. It suggests that they though it was possible to bring together large numbers (bolded because there are plenty of core gamers who have a WiiU who love it, but far fewer then 4Bone will attract in my opinion) of both core and casual gamers
There are two problems with this. First, those groups aren't the best of bedfellows, because Nintendo's family friendly image, though a very successful strategy in the Wii era is now backfiring as the sort of people who will buy 4Bone are unlikely to buy WiiU because of the 'kiddy' image. Regardless of whether or not you think this is nonsense, I think it would be difficult to deny that it exists and that whatever Nintendo did with WiiU, they would struggle to attract these people
Marketing to casuals therefore puts off these people, but if you don't do this then you won't attract the other audience. Even worse, if you comprimise too much, you won't attract either which seems to be the case with WiiU
Secondly, though there are people who love it, the GamePad is too comprimised to provide the sort of exciting new experince that Wii did because they tried to merge that kind of touch/motion gaming with traditional button-based controls and ultimately went too far that way. As a result, there isn't the same novelty factor that got all the casuals buying Wiis and so they've largley failed to attract that audience as well
This is compounded by the rise of mobile gaming - there is a larger proportion of the PS/Xbox audience who follow games more closely or feel fine with paying more for their gaming, whereas the sort of non-committed gamer who made the Wii so much more successful than the GCN don't see enough of a reason to pay the premium over their mobile games which they feel do a good enough job of entertaining them - without the novelty to attract them, they won't buy
WiiU has therefore fallen down the cracks between the old Wii audience and the 4Bone audience, and neither is particulary interested. Of course there are people who will be attracted by all Nintendo's classic IPs and the great games which are all ready there to an extent and which will inevitably continue to arrive, but not enough to match Wii.
I personally think there is only one realistic path left open to Nintendo, that is cut the price (but not necessarily by dropping the GamePad) so that you significantly undercut 4Bone - that way you will attact people in the market not prepared to cough up £350 or £430. Secondly, keep the games coming, including more deals like Bayo2, in addition to bolstering traditional 1st party development. That is the sort of game with a committed fanbase who are more likely to buy a console for a small number of games
If they can do this whilst remaining profitable, which is what they managed with the GCN then they will sell modest numbers but enough for it to be worth doing, and the console will be fondly remembered in the way that GCN is. They have to retrench, grab that core Nintendo audience and turtle out the rest of the gen like they have before. Next next gen is the key, I think a major change of approach to WiiU is needed to reach past success