Market disappointments that got hit by the smartphone tsunami but still had some very good games.

Wii U's legacy will be specifically that it's the lowest selling Nintendo console.

3DS: First handheld to have 3D Pokemon models in their main RPG
Wii U: First console with HD Nintendo games.

3DS: The last successful handheald
Wii U: Lackluster failed console with amazing games

This is the rare occasion where the "inovation" doomed the Console, those extra bucks in the GamePad moved to horsepower would make it a bit more successful, since I would not have XOne at all.

3DS - great games but full of lost masterpieces

Wii U - same as Gamecube. A console with not as expected sales but amazing games that everyone will look back onto and smile.

3DS: succesor to most popular handheld; not as original as DS, still sold a lot, gimmiky in beginning with games, great 3rd and 1st party support, handhelds not dead against mobile.

WiiU: first 8th gen console release, had year alone on market to control marketshare, failed in that aspect, good 1st party support, terrible 3rd party support, failed to continue Wii success, failed to capture hardcore gamers other than Nintendo faithful.

Nintendo's best hope for the Wii U will be for it to be called the new Dreamcast, a good system with very good to great games but arrived to early and was outmatched by its stronger generational rivals. Worst case scenario, it goes down as the dud that drove Nintendo out of the home console arena because of bad decisions in promotion and design. Time and probably the next 1-2 years of exclusives will tell.

The 3DS is likely to be a worthy successor to the DS which also helped move Nintendo into its future with more modern eShop, handheld games that rivaled console counterparts in content rather then looks and great usage of the Streetpass concept that started on the DS but reached new heights with the 3DS and hopefully beyond. Worst case scenario it is a underwhelm successor to the more popular DS with better online support. In either case for the 3DS yeah, definite success story.

3DS: One of the best if not the best handheld console of all time.
WiiU: The 2nd coming of the Gamecube.

Wii U is nowhere near Gamecube though. Gamecube was the last time Nintendo took risks. Wii U is a safe console that wanted to ride on the motion controls, when that failed, Nintendo played it safe with their big names that would sell regardless of the consoles long term fortunes. 

In terms of software, the WiiU is pretty much on the same level as the GC (minus 3rd party support).

Wii U will be remembered much like the Saturn/Dreamcast; a commercial disaster but a cult classic with plenty of hidden gems.