Depends who you ask - with much of the audience on this board and the more "core" gamers at large, many will probably say "meh". But it was a great and exciting disruptive console for its time, which drew in virtually all ages and demographics in an era when many hardcore types were purity spiraling getting out of touch with the masses in many ways and obsessing over tech. Now gaming studios are often lauded for drawing in or being inclusive to all demos, but Nintendo did it back almost 20 years ago when it wasn't considered "cool" or fashionable or a gaming-purist move to do so. While 100+ million sales may not seem like a ton now, in the context of 2006, which Nintendo coming off dwindling sales and the 21 million selling GameCube (and considering most households only tended to get one Wii unlike the Switch and the various models of other gaming consoles), it was an impressive feat that showed Nintendo managed to tap back into what made the masses tick when it comes to gaming, bringing it back to pure, accessible fun.
That said personally speaking the Wii could be a mixed bag, especially when it came to single player experiences and online. But when it comes to couch multiplayer with 4 people, it still hasn't been matched, with only the N64 coming anywhere close. It seemed like from about '06-'09 anyone remotely close in my social sphere had played Wii games with me, from my little sister to my kid cousin to my college buddies (and their buddies) to my grandmother. It was just a really cool and fun device that brought us together and made for some fun social events, hangouts, and family time.
I enjoyed the then-new concept of the virtual console and playing old classics - that was the first time I experienced some hit titles I missed before like the original Zelda, Super Metroid, Gunstar Heroes, Sonic, etc.. I also liked the intuitive pointer controls, made it feel like it merged some of the aspects I like of PC controls with console gaming.
The motion controls didn't quite work or needed to be used for everything, as shown by the often cumbersome or tacked-on feel many more traditional games on the console had. But when it came to a few genres like puzzle, party, racing, and some shooter and action games, it was impressive, meshed well and brought the experience to another level. My cousin and I playing Wii Tennis for the first time reinvigorated the gaming experience for me at a time when it was lagging (which is funny enough, currently happening to me again). It felt like picking up an NES controller and experiencing Super Mario Bros and Duck Hunt for the first time as a young lad or 5 or 6 all over again..