My little bro and sis got one for christmas. I tell you, 3 or more players in mario U is an absolute blast. We played it practically from dawn to dusk for 4 days straight. Unfortunately that's how long it took for us to beat it, so I don't know how much more play it'll get in the future. Getting a couple of people playing the platforming part of the game and one person placing blocks and stunning enemies is a riot though. Whoever is placing blocks is guaranteed to get a lot of crap from the other players when they fail to save them from a fall or something.
Nintendoland is a lot of fun too, but all of its games are so simplistic that I wonder if they'll hold anyone's interest in the long run. Zombie U was the weakest game they got, but was still pretty fun overall. The Wii U is capable of some quite nice graphics compared to other current gen consoles.