I love my Wii U. Almost everyone I know who I have shared it with is vastly surprised and it has led to a couple sales. My brother constantly begs me for mine. Its something I never expected to hear from him. He doesn't even care for the next gen stuff but he can't get enough of the old Wii U.
Having said that I don't think its going to beat the GCN. GCN was in a era where gaming media was less prominent. You can't go anywhere after launch and not hear Wii U doomed from 99% of gaming sites. Stuff like that and social media kinda fed into a anti Nintendo campaign that continues to this day. Back then I bought a GCN and almost every peripheral because the games were great and that was all that mattered. If that era was today I would have been bombarded with people telling me that it is weak and worthless and that Nintendo is Doomed. In todays era the GCN probably wouldn't have cracked 10m lifetime in sales.