Yes. I said it while it was going on and while it was released. I've been banned numerous times on this site simply because of upset Nintendo fans reporting me for saying as much.
The reason for large sales was mostly due to 'new members' to the market and it's price-point. Like a new workout style or a hot toy around Christmas, the Wii was mostly a fad and even the pattern of it's sales would suggest as much.
It had the least power and functions of all of it's competition, you could make a very strong debate that it had a worse game library overall between the three consoles (Take a look at Metacritic or other comparison sites.) It had terrible third party support even while being a market leader (indicative of the general feelings on the system). The so called "revolutionary" controls are mostly irrelevant now and much of the industry doesn't even care to utilize them in any legitimately tangible way.
Many of it's "big selling" games weren't core games at all but more of fad-esque shallow-casual games. It released the latest of all three consoles at the cheapest price and released it's successor console 'first'. It's sales were completely lop-sided and not consistent.
Absolutely was a fad and the late release of the Wii combined with the early release of the Wii U and the incredibly disappointing sales thus far for the Wii U only confirm that.