It's crazy for me to think that we've owned a Wii for a decade now. It doesn't really feel like an "old" system or anything. But damn. We got it in the summer of 2009 for our wedding anniversary. Thinking back, it's nuts how different our lives our now. In 2009 we were a couple of 20-somethings playing Wii Sports and having drinks and staying up late in our little apartment. Now we're thirty-something "grown-ups" who are sneaking some rounds of Wii Bowling while the baby's asleep.
Wii Sports harkens back to a time when pack-in games were the norm. Thinking about some of the best utilized pack-in games (SMB/Duck Hunt, Tetris); pack-in games were a way to highlight some feature of the hardware and really justify your purchase. In that respect, Wii Sports is insanely good. I mean, in an instant you "get" the motion controls of the Wii remotes. You understand how it all works, and you understand WHY they exist.
We've had a lot of fun with this game (essentially a demo disc, but totally not) over the years. Wii Tennis is still super fun as well. But Wii Bowling... that's the one we always come back to. It's a quick game to jump in and out of. And you play in quick turns. It's just so conducive to the sort of game you can sneak in between dinner and Jeopardy and still feel like you've shared a fun experience.
Also, I feel like I should at least mention that my wife is oddly good at Wii Bowling. Like, it's one of the few games that she consistently beats me in. So there's that.