I was given one of these things a couple of years ago and have picked up a handfull of cheap games at flea markets.
Honestly, this is about the shittiest game console I've played.
I know there has got to be some good games out there as I have the Mario Galaxy game on the Switch, and I like it.
Anyway, what are some hidden gems ?

Mario Kart and Call of Duty World at War

to be honest with you, they all pretty much suck. It is a game for little kids.

Wii sports and Mario karts are about the only ones I remember not being super annoying.  There was a WWII game as well, but it was awkward.

There are some games that use the controller as a gun that are fun.  You need to buy the Nintendo crossbow controller holder or an aftermarket version.  I like Link’s crossbow training and resident evil.

Our WII just collects dust.

Mario kart is really all you need.

Eta. With the expansion pack.

Mario kart
Mario party
Zelda

Skyward sword, twilight princess, resident evil 4.

Wii sports, Wii sports resort (resort is MUCH better IMO and I stopped playing the original after I got it, but you might want some of the classics like bowling, baseball, tennis)
Zeldas: Twilight Princess (my favorite of the series) and Skyward Sword

The Wii's gameplay is innovative and great, but the game library is a little lacking.  If you have one that can play gamecube games, don't forget to look there as well.  There's a lot more depth there, and in most cases they will look much better played on the Wii.  I think the later versions of the Wii dropped gamecube support.

I actually never played anything other than the ones I wrote above.  Not even mario kart.  I need to hit the used games store and fill in what I've been missing.

It was so cheesey but house of the dead was awesome on the Wii.  You'll need a gun adapter.  I used the nyko pistol.

Mad World

No More Heroes


King of Fighters collection Orochi Saga is great if you like OG 2d fighting games.
If you go for KoF you will absolutely want a more traditional controller. Preferably an Arcade stick.

Galaxy and Galaxy 2

I've been cleaning the house and found a controller, the foot pad thing, and the gun or at least the box for the gun. I didn't look. If you want it, hit me up