Alright, I'll wade into this and go with yeah, in many ways, it was a failure.
It was a flash in the pan fad with no longevity, that aged quickly (and poorly) and no staying power. Hardware flew off the shelves, it was the hottest item for Christmas for a couple of years, but compared to the PS3 and 360 they struggled to push software.
It was clear from the initial success that Nintendo wanted Wii to become a brand, like iPhone or Playststion, hence the Wii U, and in that regard they failed.
The library itself is less than stellar and whilst it has a number of interesting and unique titles, as well as hidden gems, overall it's limited. On Metacritic, just 14 Wii games have a Metacritic rating of 90 or above. Compare that to the PS3 which has 49 games with a rating of 90 or higher.
And how many Wii games do people look back at, remember fondly and are featured regularly in lists of the best games? I can think of Metroid Prime Trilogy, which is mostly an enhanced port (2 games being from the Gamecube) and the Mario Galaxy games.
The Wii has aged like milk and that's not me saying that in 2020. It had already gone sour in 2010.