I've spend hours trying to connect my Wii U to the internet and after I finally succeeded doing so so the update failed 3 times in a row at about 99%.
Some of the best functionality like backwards compatibility with wii games simply isn't possible atm.
Nintendo should provide free firmware updates to everyone. People should be able to send their consoles to Nintendo in order to get them fully updated. Because if you don't have the right ISP, router, degree in networking, location and hardware configuration you simply screwed atm.